Introduction to Animals - BIO217 Lecture Slides PDF

INTRODUCTION TO ANIMALS SUMMARY  What is an animal?  Why study animals?  General Characteristics of Animals  Phylogeny  Based on Morphology  Based on DNA analysis  Evolutionary developments WHAT IS AN ANIMAL  An animal refers any organism which belong to kingdom Animalia  A...

INTRODUCTION TO ANIMALS SUMMARY  What is an animal?  Why study animals?  General Characteristics of Animals  Phylogeny  Based on Morphology  Based on DNA analysis  Evolutionary developments WHAT IS AN ANIMAL  An animal refers any organism which belong to kingdom Animalia  Animals are a natural group (or clade) descended from a shared common ancestor.  This is monophyletic group  This clade is called the Animal Kingdom, or Metazoa. WHY STUDY ANIMALS? GENERAL CHARACTERISTICS OF ANIMALS  Every animal has almost all or all of these characteristics.  Eukaryotic Multi-cellular Ingestive Heterotrophic  Cells without walls  Unique tissues: muscles and nerves  Hox genes GENERAL CHARACTERISTICS OF ANIMALS 1. Animal are Multicellular Eukaryotic Ingestive Heterotrophs  All animals are multicellular  They are made up of more than one interdependent cells.  Development of multicellular organisms is accompanied by cellular specialization and division of labour  Cells become efficient in one process and are dependent upon other cells for the necessities of life.  All animals are eukaryotes.  They are made up of complex cell that have membrane- bound nuclei and organelles.  Their DNA is linear and organized into chromosomes.  Heterotrphs  organism, one that uses preformed organic materials as a source of energy for growth and development. GENERAL CHARACTERISTICS OF ANIMALS 2. Motility  All animals are motile at least during some stage of its life history.  Most have muscle tissues responsible for movement  Muscle tissues are unique to animals GENERAL CHARACTERISTICS OF ANIMALS 3. Rapid response to stimuli  Another unique type of cells found in most animals are nerve cells.  The nerve cells are responsible for impulse conduction.  Animals are able to respond very rapidly to stimuli because of this unique type of cells GENERAL CHARACTERISTICS OF ANIMALS 4. No cell wall  Animal cells lack the cell walls that provide support in the bodies of plants and fungi.  In plants (cellulose) and fungi (chitin), the cell wall provides structural support and protection for the cell.  Some bacteria also possess cell walls.  The multicellular bodies of animals are held together by extracellular structural proteins, such as collagen. GENERAL CHARACTERISTICS OF ANIMALS 5. Hox genes  Hox genes are a group of regulatory genes that control the timing and route of development.  They play important role during embryonic development.  Hox genes enable multicellular organisms to evolve unique body plans, each of which define an animal phylum.  Mutations in the Hox genes can lead to major morphological changes ANIMAL DIVERSITY  Animals are the most diverse living things on this planet  Of all living species on earth known to Science, approx. 75% of them are animals.  Biologists have only managed to identified 1.1 million living species of animals. ANIMAL DIVERSITY  Differences that we see among the animals is what we call animal diversity  The differences among them help us to identify them separately  The world has become beautiful due to the diversity of these animals.  We are also able to get different types of food, medicine, scents and many other necessities because of this diversity.  Now since these animals are so diverse, how do we study them? EVOLUTIONARY DEVELOPMENTS  Animal evolution is fascinating  It involves slow step-wise evolutionary changes that link the simplest to most complex  Several critical steps in animal evolution took place within the large number of invertebrate phyla. MAJOR TRENDS IN ANIMAL EVOLUTION  Animal Origins (from one cell to many)  Evolution of Invertebrates  Moving from Water to Land  Evolution of Chordates  Evolution of Vertebrates  Evolution of Amniotes EVOLUTIONARY DEVELOPMENTS Evolution of invertebrates established a number of fundamental features of higher organisms These developments led to an overall step-by-step increase in level of complexity of invertebrates EVOLUTIONARY DEVELOPMENTS Development of tissues  Parazoa (Multicellular but do not form tissues)  Phylum Porifera  Eumetazoa (form true tissues) EVOLUTIONARY DEVELOPMENTS  Eumetazoans – true tissues and body symmetry  Diploblasts – 2 embryological germ layers, ectoderm and endoderm. Only 2 Phyla left – Cnidaria and Ctenophora.  Triploblasts – 3 embryological germ layers, ectoderm, endoderm, and mesoderm. EVOLUTIONARY DEVELOPMENTS Bilateral symmetry and cephalization  Next major evolutionary event within metazoans was transition from radial to bilateral symmetry  Radial symmetry interact with environment in all sides  Difficult for animal to sense direction  Bilaterally symmetrical animal has a distinct head (anterior end) and a distinct tail region (posterior end)  Animals begin to show a concentration of nervous tissue in the anterior region (cephalization).  Cephalization occurred slowly over time and ultimately led to formation of the brain encased within a true head. EVOLUTIONARY DEVELOPMENTS The mesoderm  Evolution of mesoderm was another evolutionary advancement that arose with bilateral symmetry  Mesoderm lies between ectoderm and endoderm.  Animals with three germ layers are referred to as triploblasts  A number of tissues are derived from mesoderm  Evolution of mesoderm was an important step towards establishment of organ systems EVOLUTIONARY DEVELOPMENTS Coelom  Coelom is a body cavity which lies between the body wall and the digestive system  Acoelomates (no coelom) –  Pseudocoelomates (false coelom) –  Coelomates EVOLUTIONARY DEVELOPMENTS Complete digestive system (Tube-within-a tube)  Nematodes were some of first invertebrates to have a complete digestive system.  Porifera, Cnidaria, and Platyhelminthes all have a digestive cavity with a single opening  Presence of separate openings allows specialization of regions along the digestive tract. EVOLUTIONARY DEVELOPMENTS Body Cavity: Coelom  First animals to show a well-developed coelom were the annelids.  Coelom is a fluid-filled cavity that forms between the digestive cavity and the body wall.  The cavity is lined on all sides by mesodermal tissue. EVOLUTIONARY DEVELOPMENTS Body Cavity: Coelom This fluid filled cavity is very useful  Room for development  Shock absorber  Hydrostatic skeleton allowed organisms to move in an efficient and coordinated fashion EVOLUTIONARY DEVELOPMENTS Embryonic development  Protostome vs. Deuterostome  Cleavage of zygote  Fate of cells  Fate of pore that forms the gut during gastrulation  Embryonic origin of coelom Coelom EVOLUTIONARY DEVELOPMENTS  Protostome vs deuterostomes EVOLUTIONARY DEVELOPMENTS  Protostome vs deuterostomes EVOLUTIONARY DEVELOPMENTS  Protostome vs deuterostomes EVOLUTIONARY DEVELOPMENTS Ecdysozoa and Lophotrochozoa  Two general approaches to categorizing organisms: traditional and molecular.  Introduction of molecular methods led to changes in our understanding of evolutionary relationships between a number of invertebrate phyla  ANIMAL DIVERSITY VIEWS Two types of phylogenetic trees, morphological phylogenetic and molecular phylogenetic trees. EVOLUTIONARY DEVELOPMENTS Invertebrates to Vertebrates  Vertebrates belong to Phylum Chordata  Phylum Chordata reflects the development of notochord  Notochord serves as a major step in evolution of both internal skeleton and backbone found in vertebrates.  Other features are dorsal nerve cord, pharyngeal gill slits, endostyle and post anal tail  Evolutionary developments which occurred in metazoans prior to development of a notochord were essential for evolution of higher organisms.  EVOLUTIONARY DEVELOPMENTS  Phylum Chordata  Subpylum Urochordata  Subphylum Cephalochordata  Subphylum Vertebrata Class Common Name Characteristics Examples Agnatha Jawless fishes No jaws or scales. Lampreys, hagfish Skeletons consisting of hard, Chondrichthyes Cartilaginous fishes Sharks, rays rubber-like cartilage. Osteichthyes Bony fishes Skeletons made of bone. Tuna, bass, salmon, trout Spend part of their lives under Amphibia Amphibians Frogs, toads, salamanders water and part on land Have lungs to breathe on land, skin that does not need to be kept Reptilia Reptiles Turtles, snakes, lizards, alligators wet, and produces a watertight (amniotic) egg. Produces watertight eggs and Ostriches, penguins, flamingos, Aves Birds protects eggs from predators. parrots Nourish young with milk through Mammalia Mammals mammary glands. EVOLUTIONARY DEVELOPMENTS Evolution of Vertebrates  Within vertebrates we see evolution of complex fish Jaws  Jawless fish evolved to form jawed, cartilaginous fish and eventually bony fish. Limbs  Jawed fish evolved to tetrapods  Tetrapod classes include the following:  Amphibia  Reptilia  Aves  Mammalia EVOLUTIONARY DEVELOPMENTS Water to Land  A major evolutionary event that occurred within the vertebrates was the transition from water to land.  This required a number of physiological changes to compensate for the differences between an aquatic environment and a terrestrial environment.  On land, animals need systems to:  Support  Conservation water  Gas exchange  Reproduction  Locomotion EVOLUTIONARY DEVELOPMENTS Class Amphibia  Evolved from lobe-finned fish.  Lobe-finned fish had proto-lungs and proto-limbs.  Proto-lungs enabled them to surface from water and breath air for a short time.  Proto-limbs, or lobed fins, enabled them to walk out of the water and on land for short distances.  Amphibians evolved true lungs and true limbs for survival on land.  However, most amphibians are still dependent on water for reproduction EVOLUTIONARY DEVELOPMENTS Class Reptilia  Amphibian eggs are not truly terrestrial because they do not have a waterproof covering.  This adaptation arose with reptiles.  Reptiles have an amniotic egg.  Embryo is surrounded by layers of membranes and a solid, water-impermeable shell.  This allows embryo to survive on dry land.  Reptiles mark the full transition from water to land. EVOLUTIONARY DEVELOPMENTS Birds and Mammals  Mammals and reptiles both evolved from the same amniotic-egged ancestor  Ancestor diverged into two major groups:  Synapsids (mammalian-like reptiles)  Sauropsids (reptiles)  Dinosaurs and birds (Aves) evolved from sauropsids  Both birds and mammals are warm blooded  Birds have feathers and oviparous  Mammals are defined by presence of mammary glands in females.  Also have hair, three middle ear bones, and a specialized region of brain called the neocortex.  Most mammals also exhibit vivipary. WHY IS DIVERSITY IMPORTANT  Adaptation  Optimal utilization of resources  Diversity allows organisms to utilize different resources and environmental niches WHY IS DIVERSITY IMPORTANT  Animal diversity provides us with an array of food and materials that allows us to live healthy and happy lives  Most medical discoveries to cure diseases and lengthen life spans were made because of research into animal biology and genetics  The world has become beautiful due to the diversity of these animals THE PROTOZOA ANIMAL LIKE-PROTISTA(PROTOZOA)  All are unicellular heterotrophs.  Nutrition by ingesting other organisms or dead organic material.  Some organisms are parasitic, since they cannot actively capture food.  They must live in an area of the host organism that has a constant food supply, such as the intestines or bloodstream of an animal.  Animal Like-Protista (Protozoa) The protozoans are grouped on the basis of their modes of locomotion to: Pseudopods Flagellates Ciliates Sporozoans move by psedupodia move by flagella do not move move by cilia such as such as such as such as Amoeba Giardia Paramecium Plasmodium PROTOZOAN TAXONOMY:  Phylum Mastigophora  Phylum Sarcodina  Phylum Ciliophora  Phylum Apicomplexa MASTIGOPHORA (FLAGELLATES) E.G. EUGLENA  Characterized by presence of locomotory structures called flagellum.  Move about by beating flagellum in whip-like fashion.  Flagella have a 9+2 pattern arrangement of microtubule MASTIGOPHORA (FLAGELLATES) E.G. EUGLENA  Reproduction is asexual through longitudinal binary fission. SARCODINA (PSEUDOPODS) E.G AMOEBA o Have no wall outside of their cell membrane. o Use extensions of their cell membrane (called pseudopodia) to move and to engulf food. SARCODINA (PSEUDOPODS) E.G AMOEBA  Amoebas live in water  Nutrients from environment can diffuse directly through their cell membranes.  Most amoebas live in marine environment but some freshwater species.  Freshwater amoebas use contractile vacuoles to pump excess water out of the cell.  Most amoebas reproduce asexually by fission  Amoebas may form cysts when environmental conditions become unfavorable.  Two forms of amoebas have shells, made of calcium carbonate or silica. FEEDING  When the pseudopodium traps a bit of food, the cell membrane closes around the meal, this forms a food vacuole.  Digestive enzymes are secreted into the food vacuole, which break down the food.  The cell then absorbs the nutrients.  CILIOPHORA (CILIATED PROTOZOA) E.G PARAMECIUM  Move by cilia covering their bodies.  Found almost anywhere, in freshwater or marine environments.  Best-known ciliate is the organism Paramecium. CILIOPHORA (CILIATED PROTOZOA) E.G PARAMECIUM  Paramecia have many well- developed organelles.  Paramecia have two nuclei, a macronucleus and a micronucleus.  Macronucleus controls most of the metabolic functions of the cell.  Micronucleus controls sexual reproduction. FEEDING  Food enters cell through the oral groove where it moves to the gullet  Gullet packages food into a food vacuole.  Enzymes released into the food vacuole break down the food, nutrients are absorbed into cell.  Wastes are removed from the cell through an anal pore.  Contractile vacuoles pump out excess water, since paramecia live in freshwater surroundings. REPRODUCTION  Paramecia usually reproduce asexually, by transverse fission when conditions are favorable SEXUAL REPRODUCTION  When conditions are unfavorable, organism reproduce sexually.  This form of sexual reproduction is called conjugation.  It increases genetic diversity of the population SEXUAL REPRODUCTION  During conjugation, two paramecia join at oral groove, where they exchange genetic material.  They then separate and divide asexually  SEXUAL REPRODUCTION  During conjugation, two paramecia join at oral groove, where they exchange genetic material.  Micronucleus in each of the fused cells divide by meiosis, leading to formation of four haploid nuclei.  Out of these, three are aborted and only one survives in each cell.  SEXUAL REPRODUCTION  The surviving micronucleus again divides mitotically and forms two nuclei.  The two paramecium cells then exchange one haploid micronucleus and separate.  The new micronucleus fuses with the old to make a diploid micronucleus which then divide into eight tiny micro-nuclei.  SEXUAL REPRODUCTION  Then, the original macro nucleus slowly disintegrates, and the four micro nucleus expands to form four macro nucleus.  Later, three out of four micronucleus and macro nucleus separate, leaving the final daughter nucleus with one micronucleus and macro nucleus.  This sexual reproduction in paramecium is known as conjugation. APICOMPLEXA (SPOROZOANS PROTOZOA) E.G PLASMODIUM  Sporozoans are all parasites e.g Plasmodium  Many of these organisms produce spores  These are reproductive cells that can give rise to a new organism.  Sporozoans typically have complex life cycles  They usually live in more than one host in their lifetimes LIFE CYCLE OF PLASMODIUM THE EVOLUTIONARY CONSTRAINT OF THE CELL Factors which may have led to the development of multicellularity 1. SURFACE AREA TO VOLUME RATIO 1. SURFACE AREA TO VOLUME RATIO  Relationship between an object’s surface area and its volume determines how large a cell can grow.  Surface area is a square function, if you double an object’s size, its surface area increases by a factor of 22 or four times.  Volume is a cubic function, so if you double an object’s size, its volume increases by 23 or eight times.  As objects grow larger, their volumes increase at a much faster rate than do their surface areas. 1. SURFACE AREA TO VOLUME RATIO  Everything that comes into a cell, must come in across the plasma membrane.  Similarly everything that is expelled from a cell, must leave across the plasma membrane.  This means that the size of plasma membrane sets a limit to how quickly a cell can absorb and excrete materials.  So, the size of a cell’s plasma membrane determines how quickly it can absorb necessary substances like oxygen and nutrients, and how quickly it can expel dangerous substances like CO2. 1. SURFACE AREA TO VOLUME RATIO  The problem is that the size of the cell’s plasma membrane is a function of the cell’s surface area.  On the other hand, the amount of material inside the cell that requires oxygen and nutrients – and that generates dangerous waste products like CO2 – is a function of the cell’s volume.  So as a cell increases in size, it quickly reaches a point where it simply isn’t possible for it to grow any larger and survive. 1. SURFACE AREA TO VOLUME RATIO  If it were to grow any larger, the cell’s relatively small surface area relative to its relatively large volume would mean that it couldn’t bring in oxygen and nutrients (and expel poisonous metabolic wastes) fast-enough to keep itself alive.  So if an organism is to grow large, it must be made of many small cells,  Each of this cell has sufficient surface area relative to its volume to keep itself supplied with nutrients and oxygen, and to avoid poisoning by its own metabolic wastes. A SINGLE CELLED ELEPHANT?  No single-celled organism can grow to the size of an elephant  In fact, the largest single- celled organisms are just barely visible to the naked eye  The size limit imposed by cell size looks like one of the most probable reason why animals became multicellular!!!!!! A SINGLE CELLED ELEPHANT?  No single-celled organism can grow to the size of an elephant  Size limit imposed by cell size looks like one of the most probable reason why animals became multicellular!!!!!! 2. NUCLEO-CYTOPLASMIC RATIO A cell can have a single or multiple nuclei.  Each nucleus can only acquire a certain volume of cytoplasm.  Thus volume of a cell depends on size and number of nuclei.  And since multicellular animal are uni- nucleated there is size restriction 3. FRAGILITY OF CELL MEMBRANE  All cells have a cell membrane  Flexibility of cell membrane plays important role in processes such as exocytosis and endocytosis.  As cell increases in size the risk of cell membrane damage also increases  This limits the maximum cell size 4. MECHANICAL STRUCTURES NECESSARY TO HOLD THE CELL TOGETHER  Cells contain organelles and must remain intact  Mechanical structures must hold content together  This imposes size restriction on cell size of animals EVOLUTION OF MULTICELLULARITY From single cell Protozoan to Metazoans  PROTOZOA-COLONIAL ORGANISM  Some Protozoans live permanently in groups  A colony of single-celled organisms is known as a colonial organism.  Colonial organisms were the first evolutionary step from single-celled to multicellular organisms COLONIAL ORGANISM  All individual cells of a colonial organism can carry out all functions necessary for life  Cells of a colonial organism are identical  They are permanently associated with each other but there is little or no integration of cell activities taking place. ADVANTAGES OF COLONIAL ORGANISM  Colonial organism have following advantages:  share resources for mutual benefit  they generally improve their defenses  gain ability to attack larger prey  enhance food-gathering ability.  there may be some specialization ONE FOOT INTO MULTICELLULARITY  Colonial organisms were probably the first step towards multicellular organisms via natural selection  The difference between a multicellular organism and a colonial organism is that individual cell from a colony can, if separated, survive on their own, while cells from a multicellular life form cannot.  Cells from a multicellular organism are now too specialized to survive on their own PROTOZOA- COLONIAL ORGANISMS  Pandorina Eudoria Volvox Volvox is an example for the border between these two states. EVOLUTION OF MULTICELLULARITY  Transition from one-celled organism to multicellularity was a huge step in the evolution of life on this planet  It occurred more than once within the domain Eukarya leading to three kingdoms of multicellular life; Kingdom Plantae, Fungi (Mycota) and kingdom Animalia.  Today's plants, fungi, animals, and various types of algae are all descendants of separate transitions to multicellular life. THE COLONIAL FLAGELLATE HYPOTHESIS THE COLONIAL FLAGELLATE HYPOTHESIS  Colonial flagellate hypothesis postulate that the first animals evolved from flagellated protists that lived in colonies.  Its cells became specialized, and they started to cooperate.  By specialization and cooperation the cells combined to form a coordinated single organism with more capabilities than any of its component parts.  Many modern flagellates live in colonies, so that provides some support for hypothesis. COLONIAL FLAGELLATE HYPOTHESIS  According to this hypothesis, with time colonial cells became more and more interdependent  Cells started to specialize to perform different tasks, and became differentiated.  Eventually, cells in the colony became so specialized and interdependent that they could not no longer survive on their own.  At this point, they would no longer be a colony of cells but a multicellular organism – a simple animal.  This is how the simplest multicellular organism came into being THE COLONIAL FLAGELLATE HYPOTHESIS  These very early animals would have been quite simple by modern standards.  Over time, as cells became more specialized and interdependent, early animals would then form more complex bodies.  It was from this prototype that all animal body designs were derived  And they underwent adaptive radiation during the Cambrian explosion CHOANOFLAGELLATE CELL SPONGE AND CHOANOCYTE CELL  EVOLUTIONARY STEPS LEADING TO MULTICELLULARITY IN METAZOANS  Protozoan Colonial Metazoan organism Single cell organisms Made up of more than one cell Multi-cellular organism Made up of one formerly independent cells had to Made up of many cells, learn how to be civilized (to avoid coordination of cellular activity One cell is whole conflicts) complex organism Cooperation of cells for mutual Cellular activity integrated Cell performs all life benefit Division of labour leads to functions No cellular integration specialization and efficiency Jack of all trades and Cells still maintain their Animals can achieve big size master of everything individuality complexity and strength Size restriction imposed Cell can still survive on their Cells lose independence and by physiological processes own should they be separated from colony will die if separated  EVOLUTIONARY STEPS LEADING TO MULTICELLULARITY IN METAZOANS  Single cell Colonial Multi- organism organism cellular animal Advantages Advantages Advantages Made up of many cells, bigger sizes Division of labor and cell specialization leads to efficiency Cellular independence may be achieved Integration of cellular activity, control and Improves defenses, coordination centralized Utilize minimum Enhance food gathering abilities, Can achieve big size and complexity Longer life span lives longer, life span not linked to resources one cell Increased mechanical strength Fast reproduction No cellular activity integration, easier to coordinate  EVOLUTIONARY STEPS LEADING TO MULTICELLULARITY IN METAZOANS  Single cell Colonial Multi- organism cellular organism animal Disadvantages Disadvantages Disadvantages Require a lot of resources for Short life span, life Conflicts among cell may sustenance linked to one cell occur Takes longer to reproduce Easy predation Requires more resources Coordination of cellular activity Mechanical weaker for sustenance complex since it is made up of many cells Utilize minimum Difficult to coordinate Specialization results in cells resources cellular activity losing independence EVOLUTION OF MULTICELLULARITY  Multicellularity allows an organism to exceed the size limits normally imposed by diffusion  Single cells with increased size have a decreased surface-to-volume ratio and have difficulty in absorbing sufficient nutrients and transporting them throughout the cell.  This confers multicellular organisms with the competitive advantages of an increase in size. EVOLUTION OF MULTICELLULARITY  It also permits increasing complexity by allowing differentiation of numerous cellular lineages within an organism.  Being multicellular also benefits with having a longer life span.  Allows for sexual reproduction which increases genetic variation and can accommodate greater species adaptability to the environment. KINGDOM ANIMALIA Evolutionary history EVOLUTION OF THE ANIMAL KINGDOM  Questions regarding origins and evolutionary history of animals continue to be researched and debated  Some of these questions include the following:  How long have animals existed on Earth?  What were the earliest members of the animal kingdom  what organism was their common ancestor? PRE-CAMBRIAN ANIMAL LIFE  Animal diversity increased during the Cambrian period of the Paleozoic era (530MYA)  Time before Cambrian period is known as the Ediacaran period (620MYA to 550 MYA)  This is the final period of the late Proterozoic Era. PRE-CAMBRIAN ANIMAL LIFE  The early animal life, termed Ediacaran biota, evolved from protists at this time.  They were soft bodied animals  Some protist species called choanoflagellates closely resemble the choanocyte cells in the simplest animals, sponges.  In addition to their morphological similarity, molecular analyses have revealed similar sequence homologies in their DNA. CAMBRIAN EXPLOSION OF ANIMAL LIFE  The Cambrian period, (542–488 MYA), marks the most rapid evolution of new animal phyla and animal diversity in Earth’s history.  It is believed that most of the animal phyla in existence today had their origins during this time  We find representatives of almost all the modern phyla recognized today  This period is often referred to as the Cambrian explosion CAUSES OF THE CAMBRIAN EXPLOSION  Environmental factors  Ecological factors  Genetic and developmental factors  There is evidence that both supports and refutes each of the these  Maybe the cause was a combination of these and other theories. ENVIRONMENTAL FACTORS  The cause of the Cambrian explosion is still debated.  Some environmental changes may have created a more suitable environment for animal life.  Examples of these changes include rising atmospheric oxygen levels supporting a higher metabolic rate and allowing evolution of larger organisms and more complex body structures ENVIRONMENTAL FACTORS  Increases in oceanic calcium concentrations that preceded Cambrian period  This influx changed ocean chemistry, allowing for the first time development of hard body parts such as teeth and supporting skeletons based on CaCO3  Expansive continental shelf  Some scientists believe that a large continental shelf with numerous shallow pools provided living space for larger numbers of different types of animals to co-exist. ECOLOGICAL FACTORS  Some theories argue that ecological relationships between species may have played a role in Cambrian explosion  Factors such as changes in the food web may have contributed Cambrian explosion. o competition for food and space o predator-prey relationships GENETIC AND DEVELOPMENTAL FACTORS  Genetic and developmental factors may also have been very crucial for Cambrian explosion.  Homeobox or "hox" genes that govern developmental processes evolved prior to CE  Hox genes enabled an unique period of evolutionary experimentation  They provided morphological flexibility and complexity of animal development  This provided necessary opportunities for increases in possible animal forms. POST-CAMBRIAN EVOLUTION AND MASS EXTINCTIONS  The periods that followed the Cambrian during Paleozoic Era were marked by further animal evolution  Many new orders, families, and species emerged.  Animal phyla continued to diversify, new species adapted to new ecological niches. POST-CAMBRIAN EVOLUTION  During Ordovician period, which followed the Cambrian period, plant life first appeared on land.  This change allowed formerly aquatic animal species to invade land, feeding directly on plants or decaying vegetation. POST-CAMBRIAN EVOLUTION  Temperature and moisture also increased due to continental plate movements  This encouraged development of new adaptations to terrestrial existence in animals, such as limbed appendages in amphibians and epidermal scales in reptiles. POST-CAMBRIAN EVOLUTION  Changes in the environment often create new niches (living spaces) that contribute to rapid speciation and increased diversity.  On the other hand, cataclysmic events, such as volcanic eruptions and meteor strikes that obliterate life, can result in devastating losses of diversity.  Such periods of mass extinction have occurred repeatedly in the evolutionary record of life, erasing some genetic lines while creating room for others to evolve into the empty niches left behind. PERMIAN MASS EXTINCTIONS  End of Permian period was marked by largest mass extinction event in Earth’s history,  There was a loss of roughly 95 percent of the extant species at that time.  In oceans, phyla such as trilobites, disappeared completely.  On land, disappearance of some dominant species of Permian reptiles made it possible for a new line of reptiles to emerge, the dinosaurs.  Warm and stable climatic conditions of Mesozoic Era promoted an explosive diversification of dinosaurs.  Plants also radiated into new landscapes and empty niches CRETACEOUS MASS EXTINCTION  Another mass extinction event occurred at end of Cretaceous period  This was caused by a meteor strike  This marked the end of the Mesozoic Era  Skies darkened and temperatures fell as a tons of volcanic ash blocked incoming sunlight.  Plants died, herbivores and carnivores starved,  The mostly cold-blooded dinosaurs ceded their dominance of the landscape to more warm- blooded mammals. CENOZOIC ERA  Mesozoic Era was followed by the Cenozoic Era  Mammals radiated into terrestrial and aquatic niches once occupied by dinosaurs  Birds, warm-blooded offshoots of one line of the ruling reptiles, became aerial specialists.  Appearance and dominance of flowering plants in the Cenozoic Era created new niches for insects, as well as for birds and mammals. CENOZOIC MASS EXTINCTION  Early in the Cenozoic, new ecosystems appeared, with evolution of grasses and coral reefs.  Late in the Cenozoic, further mass extinctions  This was triggered by ice  This was followed by speciation when ice melted, leaving new open spaces for colonization. EVOLUTION OF METAZOANS From single cell to multicellular metazoans FROM SINGLE CELL TO MULTICELLULAR METAZOANS  Evolution of multi cellular sponges from single- celled protozoa is one of the landmark events in evolution.  This is the origin of the Metazoa, or multicellular organisms.  The evolution of the Metazoa from unicellular/colonial organisms occurred some 1,300–600 Myr ago in the Pre-Ediacaran period  Based on morphological characters, the transitional stages to the Metazoa suggest a colonial origin. WILSON’S EXPERIMENT  He separated cells of a living sponge by forcing it through a fine sieve.  Separated cells were let out onto a saucer containing sea-water.  Most of them were single cells.  After a while he observed that cells behaved like individual beings or amoebas.  They were crawling on the bottom of the saucer, and started joining up to form agglomerations of cells.  Eventually they grew to become whole new sponges. WILSON’S EXPERIMENT  When he tried to mash up two different species of sponges together, the separated cells mixed only with their own species.  They did not mix with the other kind of species.  This experiment may shed some light on how multi cellular animals formed initially. Phylum Porifera - Sponges Mostly marine, but include some freshwater inhabitants; usually found attached to the substratum in shallow or deep water. They are sessile; permanently attached to the substrate Obtain their food by filter feeding Simplest animals Operate at the cellular level of organization General Morphology The internal cavity is called the atrium or spongocoel Water is drawn into it through a series of incurrent pores or dermal ostia present in the body wall into a central cavity and then flows out of the sponge through a large opening at the top called the osculum Body layers 1. The pinacoderm - an outer layer of flattened cells called pinacocytes 2. An inner lining containing flagellated cells (choanocytes) - draw water in through the pores and move out through the osculum; also trap food particles that are suspended in the water. The water current is also used for gas exchange, removal of wastes, and release of the gametes  Body layers 3. Between the pinacodern and the choanocytes is a gelatinous material called mesohyl; contains several different kinds of wandering cells called amoeboid cells Archaeocytes are amoeboid cells that phagocytize food particles; they can also undergo differentiation to form other cells, including cells that produce spicules and gametes These cell are said to be totipotent The Skeleton In the mesohyl is the skeleton composed of tiny pointed structures made of silica or calcium carbonate called spicules. These structures act as an internal scaffolding, but also function in protection Among some sponges the skeleton consist of spongin fibers made of collagenous material Types of Sponges (Canal Systems) A. Asconoid Sponges Simple vaselike structure This stucture puts limitations on size; (increase in volume without a corresponding increase in the surface area of the choanocytes) B. Synconoid Sponges The flagellated choanocyte layer has undergone folding forming finger like projections There is a single osculum but the body wall is more complex, with water being received through incurrent canals, which pass it along to radial canals through to the spongocoel Results in an increase in the surface area which allowed sponges to increase in the size C. Leuconoid Sponges No atrium; several small chambers in which choanocytes are located There is a whole series of incurrent canals leading to the choanocyte chambers; water is discharges through excurrent canals Leuconoid sponges exhibit a significant increase in surface area and are, therefore, among the largest sponges Sexual Reproduction Most are hermaphroditic or monoecious. Sperm leaves a sponge via the osculum, and enters a sponge by the currents generated from the choanocytes. Fertilized eggs develop into ciliated free-swimming larvae called parenchymula or amphiblastula larvae  Asexual Reproduction Budding and fragmentation A bud or small fragment of breaks free from the parent gives rise to a new sponge. Damage to a sponge can actually promote asexual reproduction, as“parts” can land elsewhere and form new sponges. This is called fragmentation Many of the freshwater sponges can produce asexual bodies called gemmules, aggregations of cells that are enclosed in hard outer covering containing spicules Sponge Taxonomy Class Calcarea (Calcispongidae) Only sponges that possess spicules composed of calcium carbonate. Spicules are straight or have 3-4 rays. All three grades of structure- asconoid, syconoid and leuconoid. Examples are Leucosolenia, Sycon and Grantia Sponge Taxonomy Class Hexactinellida (Hyalospongiae) Glass sponges; characterized by siliceous spicules consisting of six rays intersecting at right angles Structure may be either syconoid or leuconoid. Example venus’-flower-basket (Euplectella)  Sponge Taxonomy Class Demospongiae Most diverse (more than 90%) Demosponge skeletons are composed of spongin fibers and/or siliceous spicules Siliceous spicules with one to four rays not at right angles and unfused All members express the leuconoid body form Examples: The bath sponge, Spongia and freshwater sponge, Spongilla belong to this group  All multicellular animals are called metazoans.  The first split in the metazoans resulted into two subkingdoms, Parazoa and Eumetazoa  This Split is also called the Parazoa - Eumetazoa split 1. Subkingdom Parazoa SUBKINGDOM PARAZOA- A CELLULAR LEVEL OF ORGANIZATION  There is only one phylum within this subkingdom.  This is probably first experimental lineage which never proceeded beyond the sponges.  This lineage is sometimes referred to as the evolutionary dead end because the lineage did not give rise to any other group Characteritics of the Parazoa  No true tissues or organs  No germinal layers  Intracellular digestion SUBKINGDOM EUMETAZOA Characteristics  True tissues and organs  Germinal layers present (embryos gastrulate)  Digestive cavity RADIATA-BILATERIA SPLIT  The division of eumetazoans into two branches is based partly on body symmetry  This first split which occurred in eumetazoans resulted in two branches: the radiata and the bilateria  This split is called the RADIATA-BILATERIA SPLIT TYPES OF SYMMETRY  There are two types of symmetries common in metazoans: RADIAL SYMMETRY BILATERAL SYMMETRY RADIAL SYMMETRY  Radial symmetry applies when more than two planes passing through longitudinal axis can divide the organism into mirror image halves.  Characteristic of lower animals Best suited for sessile forms RADIAL SYMMETRY  Radial symmetry takes many forms: i) Biradial symmetry – occurs where portions of the body are specialized and only two planes of symmetry sectioning can divide the animal into two halves. e.g. sea anemones RADIAL SYMMETRY ii) Multiradiality. a) quadri-radial symmetry (four planes line symmetry) e.g. jellyfishes RADIAL SYMMETRY  Penta-radial symmetry has five planes of symmetry  most sea stars display pentaradial symmetry RADIAL SYMMETRY  Majority of organisms displaying radial symmetry are sessile species (e.g. sponges and sea anemones) and pelagic species (e.g. jellyfish, ctenophores  Lower surfaces are modified to provide a stable, concrete point of attachment to some solid surface,  Upper surfaces are often modified for gathering of resources (e.g. food).  Most radial symmetrical animals move very slowly, if at all  All lateral surfaces have equal likelihood of interacting with the environment  A radial animal has no front or back end. BILATERAL SYMMETRY BILATERAL SYMMETRY  Bilateral symmetry is a condition in which only one plane running through the longitudinal and dorso-ventral axes divide the body into similar halves  There is only one plane of symmetry, which passes along the axis of the body to separate right and left sides.  This plane is called midsagittal plane.  This is the most prevalent type of body symmetry among metazoans BILATERAL SYMMETRY  Bilateral symmetry is generally found in animals with controlled mobility.  Appearance of bilateral symmetrical animal was an important innovation in animal evolution because it allowed for unidirectional movement  Bilateral organism are collectively called Bilateria  In these animals, the anterior end of body meets the environment first. BILATERAL SYMMETRY  Anterior end encounters food and danger and other stimuli first  There is a high concentration of sensory structures and nerve tissues at the anterior end.  This is called CEPHALIZATION  This is a an advantage especially for an animal which moves in the environment with its head first  Development of the head is an adaptation for unidirectional movement  BILATERAL SYMMETRY The body of a bilateral symmetrical animal is differentiated into two ends and two sides ASYMMETRY  Animals that have no plane of symmetry are said to be asymmetrical  e.g. many sponges have an irregular growth and so they lack any clear plane of symmetry.  Asymmetrical organisms lack polarity  They interact with the environment in many directions!  They are sessile PHYLUM CNIDARIA General Characteristics They are radially symmetrical; oral end terminates in a mouth surrounded by tentacles. They have 2 tissue layers Outer layer of cells - the epidermis Inner gastrodermis, which lines the gut cavity or gastrovascular cavity (gastrodermis secretes digestive juices into the gastrovascular cavity) In between these tissue layers is a noncellular jelly-like material called mesoglea Cnidarian Body Plans Polyp form Tubular body, with the mouth directed upward. Around the mouth are a whorl of feeding tentacles. Only have a small amount of mesoglea Sessile Medusa form Bell-shaped or umbrella shaped body, with the mouth is directed downward. Small tentacles, directed downward. Possess a large amount of mesoglea Motile, move by weak contractions of body Movement Cnidarian body is capable of some kind of coordinated movement Both the epidermis and the gastrodermis possess nerve cells arranged in a loose network - nerve net (plexus), which innervate primitively developed muscle fibers that extend from the epidermal and gastrodermal cells Stimulus in one part will spread across the whole body via the network Nutrition Cnidarians are carnivores with hydras and corals consuming plankton and some of the sea anenomes consuming small fishes They use they tentacles to capture prey and direct it toward the mouth so that it can be digested in the gastrovascular cavity via secretions from gland cells (extracellular digestion); some food is phagocytized by special cells and digestion occurs intracellularly The gastrovascular cavity exists as 1 opening for food intake and the elimination of waste There is no system of internal transport, gas exchange or excretion; all these processes take place via diffusion Stinging Organelles Prey capture is enhanced by use of specialized stinging cells called cnidocytes located in the outer epidermis. Each cnidocyte has a modified cilium - cnidocil, and is armed with a stinging structure called a nematocyst. The undischarged nematocyst is composed of a long coiled thread When triggered to release, either by touch or chemosensation, the nematocyst is released from the cnidocyte and the coiled thread is everted Some nematocysts function to entangle the prey; others harpoon prey and inject a paralyzing toxin Reproduction One of the most amazing adaptations is the ability of some cnidarians to regenerate lost parts or even a complete body Asexual reproduction is common with new individuals being produced by budding Sea anenomes engage in a form of asexual reproduction called pedal laceration Cnidariand are dioecious Fertilization is external, with the zygote becoming a elongated, ciliated, radially symmetrical larva - Planula larva planula larva MAJOR EVOLUTIONARY DEVELOPMENT I. TISSUE-LEVEL ORGANIZATION  The major evolutionary step that occurred with the phylum cnidaria was development of tissue-level organization.  Recall that sponges exhibit cellular-level organization but have no true tissues.  A tissue is an aggregation of similar cells that work together to carry out a specific function within the body.  This increased organization allows cnidarians to have a simple nervous system and muscle tissue.  The two simple nerve nets help coordinate muscular and sensory functions.  MAJOR EVOLUTIONARY DEVELOPMENT NERVE NET  Nerve net was an evolutionary adaptation because it was one of the first set of organized tissues.  Nerve nets can provide animals with ability to sense objects through the use of the sensory neurons within the nerve net. Nerve net is the simplest form of a nervous system found in multicellular organisms. Unlike CNS where neurons are grouped together, neurons found in nerve nets are found scattered and spread apart. MAJOR EVOLUTIONARY DEVELOPMENT NET NERVE  This nervous system allows cnidarians to respond to physical contact.  They can detect food and other chemicals in a rudimentary way. While nerve net allows the organism to respond to its environment, it does not serve as a means by which the organism can detect the source of the stimulus Stimulus in one part will spread across the whole body via the network MAJOR EVOLUTIONARY DEVELOPMENT II. RADIAL SYMMETRY  Another feature that emerges with cnidarian bauplan is radial symmetry.  Radial symmetry means that the animal can be cut in half from top to bottom at any angle to produce two identical sections.  Radial symmetry is ideal for animals that do not move or move very slowly, so they can reach into their environment on all sides. MAJOR EVOLUTIONARY DEVELOPMENT III. DIPLOBLASTICITY  Cnidarians have an ectoderm and endoderm, both of which are germ layers.  Animals with only two germ layers are called diploblastic animals.  The ectoderm produces the epidermis and the endoderm produces the covering of the digestive cavity (gastrodermis). CNIDARIAN TAXONOMY Class Hydrozoa Includes the solitary freshwater hydra; most are colonial and marine Typical life cycle includes both asexual polyps and sexual medusa stages; however, freshwater hydras and some marine hydroids do not have a medusa stage Solitary Hydras Freshwater hydras are found in ponds and streams occurring on the underside of vegetation Most possess a pedal disc, mouth, hypostome surrounded by 6-10 tenetacles Mouth opens to the gastrovascular cavity The life cycle is simple: eggs and sperm are shed into the water and form fertilized eggs; planula is by passed with eggs hatching into young hydras Asexual reproduction via budding Class Hydrozoa cont. Colonial Hydrozoans - e.g., Obelia Possess a skeleton of chiton that is secreted by the epidermis All polyps in the colony are usually interconnected Three different kinds of individuals that comprise the colony: feeding polyps or gastrozooids, defense polyps or dactylozooids and reproductive polyps or gonozooids Class Hydrozoa cont. Life Cycle of Obelia Gonozooids release free swimming medusae Zygotes become planula larvae, which eventually settle to become polyp colonies Medusae of hydroids are smaller than those of jellyfishes Also, the margin of the bell projects inward forming a shelf-like velum Class Hydrozoa cont. Other Hydrozoans Portuguese man-of-war: Single gas-filled float with tentacles Tentacles house the polyps and modified medusae of the colony Class Scyphozoa Jellyfish Medusae are large and contain massive amounts of mesoglea The differ from the hydrozoan medusa in that the lack a velum Possess four gastric pouches lined with nematocysts; these are connected with the mouth and the gastrovascular system Scyphozoan Life Cycle - Aurelia Gametes develop in gastrodermis of gastric pouches; eggs and sperm are shed through mouth Fertilized eggs develop into a planula larva; settles on substrate and develops into a polyp - scyphistoma Scyphistoma produces a series of polyps by budding - strobila The polyps undergo differentiation and are released from the strobila as free swimming ephyra Ephyra matures into an adult jellyfish Class Anthozoa (Flower animals) Exclusively marine; there is no medusa stage At one or both ends of the mouth is a ciliated groove called the siphonoglyph; generates a water current and brings food to the gastrovascular cavity Possess a well developed pharynx Gastrovascular cavity is large and petitioned by septa or mesenteries; increase surface area for digestion or support Edges of the septa usually have threadlike acontia threads, equipped with nematocysts and gland cells Class Anthozoa cont. Solitary anthozoans include sea anemones Most anthozoans are colonial (e.g. corals) and secrete external skeletons composed of calcium carbonate. Class Cubozoa (Sea wasps)  Also called boxjellies  Similar in form to the "true" jellyfish, known as scyphozoans.  Cubozoans have a square shape when viewed from above.  They also have four evenly spaced out tentacles or bunches of tentacles and well- developed eyes.  There are about 20 known species found in tropical and semitropical waters.  Australian stinger Chironex fleckeri is among the deadliest creatures in the world. TRANSITION FROM CNIDARIAN TO FLATWORMS  Cnidarians themselves were a major step forward in animal kingdom when they were invented.  They were the first to move, albeit without direction.  One ancient Cnidarian line evolved into the first flatworm. TRANSITION FROM CNIDARIAN TO FLATWORMS  Three major evolutionary developments occurred  Conversion of a two germ layer body plan (as seen in cnidarians) into a three germ layer body plan (Tribploblasty)  Triploblasty led to organ level of organization  The invention of bilateral symmetry (with distinct dorsal, ventral, left, right, anterior and posterior)  The consolidation of the nervous system into a centralized axial nerve cord, (Cephalization) TRANSITION FROM CNIDARIAN TO FLATWORMS  Three major evolutionary developments occurred  Triploblasty - conversion of a two germ layer body plan (as seen in cnidarians) into a three germ layer body plan  Triploblasty led to organ level of organization  The invention of bilateral symmetry (with distinct dorsal, ventral, left, right, anterior and posterior)  Cephalization - consolidation of the nervous system into a centralized axial nerve cord TRANSITION FROM CNIDARIAN TO FLATWORMS 1. ORIGIN OF MESODERM  Appearance of mesoderm germinal layer marked a major evolutionary advance between flatworms and lower invertebrates.  Flatworms are considered to be triploblasts because their organs develop from three germ layers: ectoderm, mesoderm, and endoderm.  This contrasts with diploblasts such as cnidarians that develop from only two germ layers: ectoderm and endoderm. TRANSITION FROM CNIDARIAN TO FLATWORMS 2. ORGAN SYSTEM LEVEL OF ORGANIZATION  Presence of a third distinct primary tissue, the mesoderm, allows flatworms and higher animals to develop distinct organ systems.  E.g., the mesoderm ultimately forms;  Muscular system –for locomotion  Reproductive – allows sexual reproduction  Nervous - allows them to sense environmental conditions  Excretory - allows them to maintain a proper balance of water and salts within their bodies TRANSITION FROM CNIDARIAN TO FLATWORMS 3. BILATERAL SYMMETRY  Distinction between a “head,” or anterior region, and a “tail,” or posterior region, resulted in a shift from radial to bilateral symmetry  Bilateral symmetry means that if the worm were sliced from top to bottom along the anterior- posterior midline, both sides (lateral halves) would be identical.  Bilateral symmetry allows animals to move more efficiently and in a more directed manner (unidirectional movement). TRANSITION FROM CNIDARIAN TO FLATWORMS 4. CEPHALIZATION  The next evolutionary change found in flatworms is termed cephalization.  Cephalization refers to concentration of nervous tissue to one end of the body, ultimately forming the head.  Flatworms were a major triumph in animal body design  They set the stage for a multitude of new bilateral species to come after them. TRANSITION FROM CNIDARIAN TO FLATWORMS Structural Differences Flatworms from Cnidarians Flatworms Cnidarians Triploblast (3 germ layers) Diploblast (2 germ layers) Organ systems No clear organ systems Cephalization (head region) No head Bilateral symmetry Radial symmetry PHYLUM PLATYHELMINTHES General Characteristics Exhibitbilateral symmetry: anterior and posterior ends are different; so are the dorsal (top) and ventral (bottom) surfaces Exhibit some degree of cephalization Bodies are dorsoventrally flattened. They are acoelomates Triploblastic Mesoderm (third germ layer) gives rise to muscles, organ systems, and the parenchyma CNS Protonephridia No respiratory + circulatory system Outer Body Covering body is covered by a ciliated epidermis (Turbellarians) Epidermal cells contain rod-shaped structures called rhabdites The outer body covering of other platyhelminthes (e.g., parasitic forms) is a non-ciliated tegument The tegument is referred to as a syncytial epithelium Organ Systems of the Platyhelminthes Digestive System Some of the flatworms possess a digestive system, with a mouth, pharynx, and a branching intestine from which the nutrients are absorbed Digestive system, with only one opening, is a blind system or incomplete ORGAN SYSTEMS OF THE PLATYHELMINTHES CONT. Excretory System (osmoregulation) A network of water collecting tubules adjacent to flame cells or a protonephridia When cilia beat they move water into the tubules and out the body through pores called nephridiopores Flame cells consist of a hollow cup filled with cilia that beat and pump water and nitrogenous wastes out the body Organ Systems of the Platyhelminthes con’t Muscular System Below the epidermis are layers of circular and longitudinal muscle fibers; used in locomotion Nervous System The have a CNS Includes: anterior cerebral ganglia, longitudinal nerve cords, and some lateral nerves Most free living planarians and parasitic larval forms possess a variety of sensory organs (e.g., eye spots, statocysts, rheoreceptors) ORGAN SYSTEMS OF THE PLATYHELMINTHES CONT. Reproductive System Most flatworms are hermaphrodites Reproduction occurs with the reciprocal exchange of sperm Fertilized eggs are released and usually develop directly into flatworms Most are capable of some form of asexual reproduction (e.g., many turbellarians reproduce by fission) Most species possess remarkable powers of regeneration PLATYHELMINTHES TAXONOMY  PHYLUM PLATYHELMINTHES Planarian Monogenian 17 Flukes Tapeworms  Class Turbellaria Free-living flatworms; mostly marine organisms Range in size from microscopic (interstitial species between sand grains) to extremely large (two feet) Locomotion Most move by means of cilia and mucous Muscle contractions also permit turning, twisting and folding of the body Class Turbellaria con’t Nutrition Turbellarians are carnivores and prey on other animals or eat dead animal remains. Planarians have a muscular pharynx that they can insert into their prey and then pump to bring in food fragments These animals have a highly divided gut to greatly increase the surface area for digestion and absorption Senses They have well developed sensory structures, including eyespots, mechanoreceptors, and chemoreceptors Class Turbellaria con’t Reproduction Planarians are capable of asexual reproduction via fission Also capable of regeneration; exhibit both anterior- posterior and lateral polarity They are hermaphrodites but usually exhibit cross-fertilization The penis of some turbellarians is modified as a hollow stylet; sperm tranfer is by hypodermic impregnation, in which the copulating partners stab each other and inject sperm Class Monogenea (Monogenetic fluke) Most species are ectoparasitic There are 3 endoparasitic species: one in the coelom of elasmobranchs, one in the ureter of freshwater fishes, and one in the urinary bladder of amphibians General Characteristics Ectoparasitic species are usually attached to the gills, scales and fins of fishes; highly site specific Possess a holdfast sucker(s) at the posterior portion of the body - opisthhaptor; may possess hooks or anchors (hamuli) General Characteristics cont. In certain monogeneans, the haptor is adapted to hold onto the second gill lamellae of the host fish In these forms, the haptor is divided into a series of sucker like arms And may be strengthened with chitinous sclerites called clamps General Characteristics cont. The anterior end of the body - prohaptor - has various adhesive and feeding organs There are 2 main types of prohaptors: those that are not connected with the mouth funnel and those that are With the first case the head end is truncated, lobated or broadly rounded These worms often bear head glands which are important adhesive devises The second type of prohaptor has specializations of the mouth and buccal funnel; the simplest types have an oral sucker that surrounds the mouth General Characteristics cont. All monogeneans have a mouth, pharynx, bifurcated intestine, and cecae; there is no anus Monogeneans on scales and tail fins of fishes feed on mucus Those that occur on gills feed on blood (from the branchial capillaries) Life Cycle Monogeneans have a direct life cycle (no intermediate host) Eggs hatch and give rise to a oncomiracidium, a ciliated larvae that bears numerous hooks Thus the larva is adapted for both swimming and attachment The larvae attach onto the host via their haptor as soon as they come into contact with the host’s skin or gills These larvae have a life span of about 12-24 hrs There are several interesting variation of the general reproductive styles of monogeneans Gyrodactylus elegans only monogenean that is viviparous females give birth to live young and die Gyroductylus elegans produce four succeeding generations in one ovum. Gyrodactylus elegans) Diplozoon paradoxum (1cm). Parasite of fish Juveniles do not become sexually mature until they meet a partner of opposite sex. They then achieve sexual maturity and mate Two animals form a permanent union, joined near their midsections. Class Trematoda (Digenetic flukes) Flukes that live as parasites either on or in other organisms. Outer body lacks cilia; tegument has a layer of glycoproteins that are important in protection and absorption Possess 2 suckers: 1. Oral sucker which attaches to organs of the host 2. Ventral sucker or acetabulum; used to attach to host tissues Types of Hosts Often have complex life cycles that alternate between sexual and asexual stages. Most require at least 2 different kinds of hosts to complete their life cycle: 1. Definitive host (primary host) The host in which the parasite matures and reproduces (sexually) The host in which eggs are released 2. Intermediate host Hosts in which larval stages develop and undergo asexual reproduction Results in an increase in the number of the individuals General Life Cycle - Chinese liver fluke, Clonorchis sinensis Adults live in the bile ducts of humans, dogs, and cats There are 2 intermediate hosts: a snail and a fish Eggs are passed out of the definitive host and hatch as ciliated larvae called miracidia The miracidia penetrates a snail molluscan host and becomes a sporocyst They undergo asexual reproduction producing larvae called rediae Rediae often asexually produce more rediae, but will eventually give rise to larvae called cercariae They leave the molluscan host and penetrate fish They encyst in the fish tissues as the metacercaria Consumption of infected fish results in the metacercaria excysting in gut and migrating to the bile duct Schistosoma Schistosoma spp. is a common blood fluke of Southeast Asia that causes shistosomiasis Humans are the definitive host; snails are the intermediate host In humans its eggs ultimately penetrates and damages intestinal tissue and tissue of the bladder A source of constant inflammation and eventually leads to deterioration of liver, spleen and other organs Class Cestoda General Morphology Non-ciliated tegument composed of glycoprotein Anterior region is called a scolex; often armed with suckers and hooks Extending from neck is a series of proglottids; contain the sex organs and eggs; no digestive system Mature eggs released through an opening in the proglottid or leave the host when proglottids are separated from main body of the worm. Beef Tapeworm, Taeniarhynchus saginatus Definitive host humans; intermediate host cattle Eggs are shed with human feces; infected persons defecate in a pasture and the eggs are ingested by cattle Eggs hatch giving rise to oncosphere larvae that bore into the intestinal wall and get into the circulatory system to be transported to muscle Here the larvae develop into the cysticercus stage (=the bladder worm) with the inverted scolex If uncooked beef is consumed the cysticercus is freed and the scolex everts, forming the adult Symptoms include loss of weight, chronic indigestion, diarrhea TRANSITION FROM FLATWORMS TO NEMATODES TRANSITION FROM FLATWORMS TO NEMATODES  Flatworm have a solid body design called the an acoelomate bauplan  There is no space between the body wall and the digestive system  Organs are embedded within solid mesodermal tissue called mesenchyma  Body is evolutionary constrained to be flat  Next step during evolution of metazoans was to develop a space between body wall and gut  This space is called a coelom TRANSITION FROM FLATWORMS TO NEMATODES  Two major developments occurred  Tube-within-a-tube body design – separates the digestive system from the body wall  This bauplan resulted in two major improvement in the body design:  Development of a body cavity (Coelom) - Pseudocoelom  Development of a complete digestive system – There is one way movement of food. This allows different regions to become specialized. It also allows them to eat, digest food, and eliminate wastes all at the same time.  THE PSEUDOCOELOM BAUPLAN 1. This is a space derived from what was the blastocoel during embryogenesis 2. Pseudocoelom provides space for the various internal organs. 3. Pseudocoelom with coelomic fluid serves as ‘hydrostatic skeleton’ during locomotion. 4. Coelomic fluid protects the internal organs from mechanical shocks. 5. The coelomic fluid helps in distribution of the nutrients, collection and storage of nitrogenous wastes before excretion. 6. Separation of body wall (somatic tube) and gut tube (visceral tube)- ‘Tube-within-a-tube’ PHYLUM NEMATODA  Nematodes (Greek, thread)  They are considered to be PSEUDOCOELOMATES because their body cavity is not fully lined with a mesoderm.  They lack MESENTARIES, linings and membranes that SECURE INTERNAL ORGANS.  They are called round worms  CHARACTERISTICS a. TRIPLOBLASTIC, bilateral, VERMIFORM (resembling a WORM shape), UNSEGMENTED, pseudocoelomates, mild cephalization with primitive BRAIN b. Body is ROUND in cross section and covered in a CUTICLE CHARACTERISTICS a. COMPLETE digestive system, mouth usually surrounded by lips bearing sense organs b. Excretory system composed of RENETTE cells. Have no BLOOD or GAS EXCHANGE systems. c. Body wall has only LONGITUDINAL muscles CHARACTERISTICS Eutely (cell constancy) – same number of cells for each animal and for each given organ in all the animals of the species Ex. Caenorhabditis elegans (a type of nematode) has 959 cells Every worm in the species has 80 cells in their pharnyx  EXTERNAL FEATURES  The nematode body form is VERMIFORM. That is, that it resembles a WORM. It is elongated, slender, cylindrical and tapered at both ends.  THE CUTICLE  Nematodes have a NONCELLULAR, protective, organic layers secreted by the epidermis called CUTICLE.  Cuticle may be smooth or contain spines, bristles, and ridges.  It resist very HIGH HYDROSTATIC pressure exerted by fluid on pseudocoelom.  It also is used for protection in parasitic nematodes because it is resistant to DIGESTION.  They grow by MOLTING THE LONGITUDINAL MUSCLES LONGITUDINAL MUSCLES: the principal means of LOCOMOTION in nematodes. The contraction of these muscles result in undulated waves that pass from the anterior to posterior end of the animal. This gives the round worms their characteristic THRASHING movements. Because they lack CIRCULAR MUSCLES they are unable to CRAWL like other worms. SENSORY ORGANS. Nematodes contain two main sensory organs i. AMPHIDS: ANTERIOR depressions in the CUTICLE that contain CHEMORECEPTORS. ii. PHASMIDS: POSTERIOR CHEMORECEPTORS near the ANUS iii. Ocelli – found in aquatic forms ONLY INTERNAL FEATURES:  The nematode pseudocoelom is a spacious, FLUID FILLED cavity that contains the visceral organs and forms a HYDROSTATIC skeleton. FEEDING AND DIGESTION  Nematodes feed on any source of organic matter whether living or dead.  They play an important role in the processing of soil and some cause human and crop diseases.  Therefore they are highly studied for their medical and agricultural impact COMPLETE DIGESTIVE SYSTEM i. Nematodes have a complete digestive system ii. They have a tubular digestive tract that extends from anterior mouth to posterior anus iii. The PHARYNX is muscular that moves the food through the system. iv. This is the first time that organisms have been able to INGEST food, DIGEST it, ABSORB its nutrients, and PASS it out as feces in one SEQUENTIAL motion. This is a huge advantage to the nematodes and high order organisms. COMPLETE DIGESTIVE SYSTEM  Complete digestive system can hold more food since animals eating continuously, allowing them to extract more nutrients.  The second advantage of a complete digestive tract is its efficient absorption of nutrients.  Since the digestive tract is a long tube, organisms can house lots of organs. EXCRETORY SYSTEM  Nematodes have a waste management system that is made of glandular cells called RENETTES  Two systems exist: Glandular and tulular type  Glandular type- renettes absorb waste from pseudocoelom and empty it outside body through excretory pore  Tubular type – renettes all empty into a common canal  Wastes is the excreted outside through an excretory pore NERVOUS SYSTEM  Nematodes have an anterior primitive brain called a NERVE RING.  Nerves extend both anteriorly and posteriorly  Nematodes have two nerve cords in their body; ventral (belly) and dorsal (back) nerve cords  Nervous system allows nematodes to detect its environment and react to it REPRODUCTIVE SYSTEM  Most nematodes are DIOECIOUS and dimorphic, with the MALES being SMALLER than the FEMALES.  Males can be identified by a CURLED posterior end  Nematode sperm are amoeboid cells and their motility is driven by pseudopodium Important Nematode Parasites of Humans FILARIAL WORM  FILARIAL Worm is transmitted by MOSQUITOS and causes (FILARIASIS) ELEPHANTIASIS which results in the enlargement of various appendages due to the blockage of the LYMPH SYSTEM. FILARIAL WORMS  Threadlike nematodes inhabiting lymphatic vessels and other tissues sites in vertebrate hosts such as birds and mammals  They have an infective stage called microfilaria  Their life cycle requires an arthropod intermediate host  Females are ovoviviparous  Blood sucking insects such as mosquitoes and fleas are intermediate hosts  A number of species parasitize humans causing a disease called filariasis  In Africa and Asia, the most common nematode causing filariasis is Wuchereria bancrofti Wuchereria bancrofti (bancroftian filariasis)  Bancroftian filariasis is commonly called "elephantiasis."  Adult parasites live in lymph nodes of humans  Female worms produce microfilariae that are found in the blood.  Microfilariae are ingested by a mosquito when it feeds  In mosquito microfilariae transform into infective larvae.  When mosquito feeds again on a human, the infection is transmitted via the larvae.  Larvae migrate to the lymph nodes, reach sexual maturity, and the life cycle is complete.  Several genera of mosquitoes will transmit this parasite, including Anopheles, which is also a vector for malaria (Plasmodium spp.). HOOKWORMS  Hookworms are named for their teeth with they use to slice into and grab onto the intestine of their host Once ‘hooked in’ the parasite make more cuts into the victim’s intestine and drink the blood that flows out May have a lifespan of 1 to 9 years HOOKWORMS  These little blood sucker are true devils  They use their claw-like teethe to attach and the suck down as much blood as they can Hookworm can have devastating effects on humans, particularly children, due to the loss of excessive amounts of blood. One hookworm can imbibe more than 0.6 ml of blood per day. Someone with an infection of 100 hookworms would be losing approx. 60 ml of blood daily. Infections of 1000 hookworms per host are not uncommon. A heavy infection can produce serious damage to the host through loss of blood and tissue damage HOOKWORMS  Many species of hookworms infect mammals.  Most important, for human are:  Ancylostoma duodenale  Necator americanus,  the dog and cat hookworms are:  Anylostoma caninum (Dogs)  Ancylostoma braziliense (cats)  Hookworms average about 10 mm in length and live in the small intestine of the host.  LIFE CYCLE  Males and females mate, eggs that are passed in feces.  Female hookworms can produce 10,000-25,000 eggs per day.  About two days after passage eggs hatches, and the juvenile worm (or larva) develops into an infective stage in about five days.  Next host is infected when an infective larva penetrates host's skin.  Juvenile worm migrates through host's body and finally ends up in the host's small intestine where it grows to sexual maturity. ASCAROIDS  ASCARIS: The GIANT INTESTINAL ROUNDWORM causes the disease ASCARIASIS which can result in the blockage of the intestines. ASCAROIDS  Ascaroids feed on intestinal contents of humans, domestic animals and other vertebrates.  They are entirely parasitic within a single host.  One of the most common ascaroid which infects about 25% of the world’s population is Ascaris lumbricoides Adult females can measure between 20 to 35 cm long Males are 15 – 30 cm Adult worms live in small intestine and eggs are passed in feces. ASCAROIDS  A single female can produce up to 200,000 eggs each day!  About two weeks after passage in feces eggs contain an infective larval stage  humans are infected when they ingest such infective eggs.  Eggs hatch in small intestine  Juvenile penetrates small intestine and enters circulatory system, and eventually enters lungs.  ASCAROIDS  In lungs juvenile worm leaves circulatory system and enters air passages of lungs.  Juvenile worm then migrates up air passages into pharynx where it is coughed up and swallowed  Once in small intestine juvenile grows into an adult worm. Worm cause serious pathology Worms may physical block gut Host may starve May cause ‘ascaris pneumonia’ migration of larvae through lungs causes blood vessels of lungs to bleed, and there is an inflammatory response accompanied by edema. OTHER NEMATODES OF IMPORTANCE  Enterobius vermicularis  Trachinella spiralis  Trichuris trachiura  Strongyloides stercoralis The Pseudocoelom Bauplan The Pseudocoelom Bauplan Advantages of pseudocoelom 1. Pseudocoelom provides space for internal organs. 2. Pseudocoelomic fluid serves as ‘hydrostatic skeleton’ during locomotion. 3. The coelomic fluid protects the internal organs from mechanical shocks. 4. The coelomic fluid helps in distribution of the nutrients, collection and storage of nitrogenous wastes fill the time of excretion. Pseudocoelomate Phyla  Acanthocephala -- spiny-headed worms; about 1150 spp  Chaetognatha -- arrowworms; about 70 species.  Cycliophora -- cycliophorans; 1 species known  Gastrotricha -- gastrotrichs; about 430 species known  Kinorhyncha -- kinorhynchs; about 150 species known  Loricifera -- loriciferans; about 10 species described  Nematoda -- nematodes or roundworms; about 12,000 spp  Nematomorpha -- horsehair worms; about 320 species  Priapulida -- priapulid worms; 16 species known  Rotifera -- rotifers or "wheel animalcules"; about 1500 spp THE EUCOELOMATE BAUPLAN  Coelom body design was redesigned in eucoelomates  Coelom now surrounded by mesodermal tissue  Presence of mesodermal epithelial layer over digestive system provided with musculature which facilitates peristaltic movements in alimentary canal  Because of this ingestion of food and egestion of waste is made easy THE EUCOELOMATE BAUPLAN EUCOEOLMATES  Cavity that is present in between body wall and the gut is lined on either side by epithelial layers is called Eucoelom or true coelom.  It is lined by means of mesoderm.  The coelomic epithelium present below the body wall is referred as parietal layer or somatic layer.  Coelomic ephithelium present above gut wall is referred as visceral layer or splanchnic layer.  Both the layers are mesodermal in origin. EUCOEOLMATES  Based an the mode of formation of coelom, coelomates are classified into two types; they are:  1) Schizocoelomates 2) Enterocoelomates. SCHIZOCOELOMATES: The cavity formed by the splitting of embryonic mesoderm is called ‘Schizocoelom’, Animals are referred as Schizocoelomates. E.g. :Annelida, Arthropoda , Mollusca. LESSER PROTOSTOMES  Phylum Sipuncula  Phylum Echiura  Phylum Phoronida  Phylum Brachiopoda  Phylum Ectoprocta  Phylum Pentastomida  Phylum Onychophora  Phylum Tardigrada  Phylum Chaetognatha  Phylum Pogonophora SCHIZOCOELOMATES:  In Schizocoelomates the zygote exhibits spiral cleavage.  Embryonic mesoderm is formed through teloblastic method.  In this method a single micromere called 4d blastomere or mesentoblast cell present at the rim of blastopore proliferates to form mesoderm between the developing archenteron (endoderm) and the body wall ( ectoderm), in the blastocoel. SCHIZOCOELOMATE BAUPLAN ENTEROCOELOMATES  In Enterocoelomates the lumen from the archenteron extends into the mesoderm in the form of pouches to form coelom.  So the coelom is referred as enterocoelom. Examples:  Echinoderms,  Hemichordates  Chordates  ENTEROCOELOMATES  In the embryonic condition, archenteron produces a pair of lateral pouches.  These pouches get pinched off from the archenteron into the blastocoel.  The cavity within these pouches is the enterocoelom.  As these pouches enlarge and fuse, the blastocoel is replaced into somatic layer below the body wall and splachnic layer above the alimentary canal. ENTEROCOELOMATE BAUPLAN  ADVANTAGES OF EUCOELOM  1. Due to presence of mesodermal epithelial layer over the digestive system alimentary canal is provided with musculature.  This facilitates peristaltic movements in alimentary canal;. Because of this ingestion of food and egestion of waste is made easy.  2. Due to presence of large space /coelom alimentary canal get elongated so that the absorptive surface of the canal has increased. ADVANTAGES OF EUCOELOM  3. Eucoelom furnishes space for the accumulation of nitrogen waste and excess water. These can be discharged by the excretory ducts.  4. The gonads projects into the coelom, ample space is provided for the enlargement and production of large yolked eggs. EMBRYONIC DIFFERENCES BETWEEN PROTSOSTOME AND DEUTEROSTOME METAMERISM  Metamerism is a Greek term meaning meta=later, mere = part.  Metamerism is the condition when the general separation of bilateral animals involves longitudinal division of the body into linear series of similar sections.  Metamerism is also known as metameric segmentation.  Each section is called metamere or somite or segment.  Each of these segments has repeats of some or all units of organs. METAMERISM  The primary segmental divisions are body wall musculature and coelom.  This in turn imposes a corresponding metamerism on the associated systems.  Longitudinal structures like gut, main blood vessels and nerves extend through entire length of the body.  Structures like gonads are repeated in all or only few segments. METAMERISM  Metamerism in Animal Kingdom include, metamerism encountered for the first time in annelids.  Apart from this it is also found in phylum Arthropoda and Vertebrata.  One group of Mollusca (Monoplacophora) also exhibits metamerism.  Tape worms show pseudometamerism or strobilization, which is not true metameric segmentation. TYPES OF METAMERISM External and internal metamerism:  In most of the Annelids, metamerism is conspicuously visible both externally and internally.  Even coelom is segmentally divided into compartments by intersegmental transverse mesenteries called septa.  Only digestive tract escapes this metamerism and it extends through every segment.  In Arthropods, metamerism is chiefly external.  Humans and other vertebrates show internal metamerism of nerves, blood vessels etc. TYPES OF METAMERISM Complete and incomplete metamerism:  Complete type of metamerism affects all the body systems.  In this type metameres are homonomous and each metamere has segmental blood vessels, nerves, coelomoducts and nephridia.  This condition is also called homonomous metamerism.  Metamerism in Arthropods and other higher animals is incomplete because of division of labour.  Different regions of the body vary considerably.  Such a condition is called heteronomous metamerism. TYPES OF METAMERISM True and pseudometamerism:  True segments in Annelids are developed during the embryonic stages whereas the pseudosegments present in tapeworms are superficial which are formed as a result of strobilization.  The proglottids of tapeworms are not true segments but rather they are complete reproductive individuals. TYPES OF METAMERISM True Metamerism Pseudo Metamerism Number of segments is constant for Number of segments is not constant as each species. No new segments are new segments are constantly added added except in asexual reproduction. throughout the life. Simple elongation of the preexisting Addition of new segments from segments results in growth. proliferation region results in growth. All the segments are of same age and Proglottids vary from one another in at same stage of development. age and degree of development. All the segments are integrated and The proglottids are independent and interdependent functionally. They self-contained units as each of them work in coordination and preserve the have full set of sex organs, excretory individuality of the body. This and nervous systems. Each proglottid individuality of the body helps in is productive unit developed for locomotion. detachment. SIGNIFICANCE OF METAMERISM  It provides an effective locomotory mechanism as coordinated contraction along body generates efficient body undulating movement.  Fluid filled coelomic compartments provide hydrostatic skeletons for burrowing. Accurate movements can take place by differential turgor pressures affected by flow of coelomic fluid from one part of the body to the other.  Different segments can be specialized for different functions leading to the development of high grade of organization. It is not clearly marked in annelids, but well developed in arthropods (tagmosis). Metamerism Body is divided into a linear series of similar parts or segments, and each segment is called a metamere. The pattern of repeated segmentation is called metamerism Each metamere is separated from the next by a transverse septum Each metamere acts as a hydrostatic skeleton Each metamere has longitudinal and circular muscles; longitudinal muscle contraction causes segments to shorten; circular muscle contraction causes segments to elongate Each segment usually bears one or more chitinous bristles called setae; help anchor segments Have an anterior prostomium and posterior pygidium; both non-segmented PHYLUM ANNELIDA Metamerism Have an anterior prostomium and posterior pygidium; both nonsegmented Body is divided into a linear series of similar parts or segments, and each segment is called a metamere The pattern of repeated segmentation is called metamerism Each metamere is separated from the next by a transverse septum Each metamere acts as a hydrostatic skeleton Each metamere has longitudinal and circular muscles; longitudinal muscle contraction causes segments to shorten; circular muscle contraction causes segments to elongate Each segment usually bears one or more chitinous bristles called setae; help anchor segments Advantages of metamerism 1. greater flexibility of movement, compare to nematode 2. Components organ systems repeated w/i segments – (repeated excretory, nervous, circulatory structures) – Built-in redundancy- increases survival Nervous System  Greater flexibility demands greater fine motor skills  Highly developed, centralized nervous system  brain  Ventral longitudinal nerve cord  Ganglion in each metamere Circulatory System Closed circulatory system, in which the blood is always enclosed within blood vessels that run the length of the body and branch to every segment Several hearts (5 in earthworms) are used to pump blood through the closed circuit Closed circulatory system of Annelids Annelida , the heart and blood vessels form a closed system 1. Blood flows through closed vessels 2. Blood flows at a very high velocity 3. Haemocoel is absent 4. Internal organs are not in direct contact with blood 5. Blood takes short time to complete 6. Supply and elimination of materials are very rapid 7. Exchange of materials between blood and tissues takes place through the capillaries 8. Blood flow can be regulated Excretory System Consists of paired (metameric) metanephridia Excretory tubes with ciliated funnels that remove waste from the coelomic fluid; open to the outside via excretory pores. Note: Not all organ systems are metameric E.g., the digestive system extends the length of the organism and is differentiated along its length Reproductive System Most annelidsare hermaphroditic, but they are usually cross fertilizers. Earthworms and leeches form pairs and reciprocally fertilize one another Some annelids (e.g. marine sandworms) are dioecious and they release eggs and sperm into the marine environment, where gametes unite to form trochophore larvae Class Polychaeta (many bristles) General Characteristics Marine worms, including sandworms and clamworms. Each segment is equipped with a pair of fleshy paddle-like structures - parapodia; used in locomotion Parapodia contain a large number of chitinous bristles – setae; anchor the worms Polychaetes: General Characteristics cont. Prostomium is well equipped with sensory and feeding structures Polychaetes: General Characteristics cont. Mouth is located just below the prostomium, but in front of the modified segments - peristomium Digestive system includes a muscular pharynx that can be everted through the mouth Pharynx is equipped with pincer-like jaws Although many of the smaller polychaetes lack respiratory structures, the larger one do possess gills Gills are usually modifications of the parapodia Class Polychaeta: Diversity Although a number of polychaetes are active predators, some are sedentary and burrow into mud or live in protective tubes in the mud In several of these species filter feeding has evolved A good example is the fan worm Sabella, with their feather-like head structures called radioles Class Polychaeta: Diversity cont. Chaetopterus is tube dweller; lives in a U-shaped tube Parapodia are highly modified into 3 fan-like structures that bring water into the tube The notopodium secretes a mucous bag that traps food from the water flowing through the tube; the bag is periodically passed anteriorly toward the mouth Class Polychaeta: Diversity cont. Arenicola lives in a J-shaped burrow It employs peristaltic movements to generate a water flow Food is filtered out from the front of the burrow Class Oligochaeta ("few bristles") Many of the morphological structures are reduced when compared to the polychaetes Prostomium lacks sensory structures Parapodia are absent; each segment usually contains one or more pairs of setae; used in locomotion Aquatic forms usually have larger setae than the terrestrial forms Class Oligochaeta cont. Earthworms feed on vast quantities of soil that contains living and decaying organic material. Digestive tract of the annelids shows specialization along its length: mouth, pharynx, crop (food storage), gizzard (grinding), calciferous glands (accessory glands that excrete excess calcium from the food) Remainder of the gut is the intestine - for digestion and absorption Its surface area is increased because of a dorsal longitudinal fold called the typhlosole Class Oligochaeta cont. Lack respiratory organs; gas exchanges occurs across the body wall Hermaphroditic, but exchange sperm during copulation During copulation, worms join their anterior ends; held together by mucous secretions from a clitellum After reciprocal copulation, sperm is stored in seminal receptacles Clitellum then secretes a mucous tube that serves as a cocoon The cocoon moves anteriorly and eggs from the oviduct and sperm from the seminal receptacles are poured into it; fertilization occurs in the cocoon Cocoon eventually slips off the anterior end of the worm In time, young worms emerge from the cocoon Class Hirudinea Body is dorso-ventrally flattened Anterior segments are modified as a small sucker which surrounds the mouth; posterior segments form a larger sucker Setae are completely absent Evidence of segmentation externally, but no internal septa There is serial repetition of many of the organs (e.g., nephridia and testes) Class Hirudinea cont. Leeches crawl over the surface in a loop like fashion, with the use of 2 suckers. Body is extended due to circular muscle contraction and the attachment of the anterior sucker to the substrate. Posterior sucker is subsequently released, and longitudinal muscles contract bringing the posterior part of the body forward. Class Hirudinea con’t Most leeches are active predators; however, some are the parasitic, bloodsucking forms. Blood suckers have blade like jaws that they use to penetrate the skin of a host. Blood is prevented from clotting because they secrete a powerful anticoagulant; anesthetics are also released A muscular pharynx subsequently pumps blood into the gut. MEDICINAL LEECHES Produce very important compounds in their salivary glands. Antibiotic (treat bacterial infections) Anaesthetic (prevent prey from feeling pain) Anticoagulant Hirudin (inhibit blood clotting) Hementin (dissolve blood clot) Orgelase (enhances blood circulation. Class Hirudinea con’t Leeches are hermaphroditic but engage in cross-fertilization; some use hypodermic impregnation Leeches have a clitellum and are capable of generating a cocoon PHYLUM ARTHROPODA  Arthropod Taxonomy: Overview The arthropods evolved along four main lines, which most zoologists recognize as 4 distinct subphyla 1. Trilobita - extinct trilobites 2. Chelicerata - horseshoe crabs, spiders, ticks, mites, and some extinct groups 3. Crustacea - crabs, lobsters, shrimps, barnacles 4. Uniramia - insects, centipedes, millipedes  The Arthropod Exoskeleton Epidermis secretes an external skeleton called the exoskeleton Advantages of possessing an exoskeleton: – provides strong support – provides rigid levers that muscles can attach to and pull against – offers protection – serves as a barrier to prevent internal tissues from drying out; important because many arthropods live on land – serves as a barrier to prevent infection Structure of the Exoskeleton Composed of the polysaccharide chitin and protein - glycoprotein Outer surface called the epicuticle; contains waxes The thicker portion is called the procuticle: exocuticle endocuticle In the exocuticle, the glycoprotein chains are cross linked; process is called tanning epicuticle exocuticle procuticle endocuticle epidermis Molting Inorder to grow the arthropod must shed its exoskeleton, and secrete a new and larger one - molting or ecdysis. Jointed Appendages Exoskeleton divided into a number of plates and cylinders At the junction point between plates and cylinders, the exoskeleton remains thin and flexible; these are the joints Jointed appendages allows arthropods to move efficiently and quickly Muscles are integral to arthropod movement; they attach to the inner side of the exoskeleton; they often function as a lever system Arthropod joint Vertebrate joint Specialized Arthropod Segments: Reduction in Metamerism The evolution of the arthropods witnessed a reduction in metamerism The arthropods evolved modified groups of segments (e.g., segments became lost, some fused together The fusion of groups of segments into functional groups is called tagmatization In so doing, various appendages on segments became specialized for functions other than locomotion, e.g. prey capture, filter feeding, sensing various kinds of stimuli, gas exchange, copulation, etc.  Arthropod Respiratory Advances Special respiratory structures allow the arthropods to metabolize more efficiently and thus move rapidly High metabolic rates require rapid oxygen delivery, and arthropods can accomplish this with respiratory organs that have a large surface area for collecting oxygen quickly Gills Many aquatic arthropods (crabs and lobsters) have gills, which are typically modifications of appendages or outgrowths of the body wall - folds of tissue with a large surface area Tracheae Gasexchange organs among terrestrial arthropods is usually internal; invaginations of the integument Insectshave tracheae, branching networks of hollow air conducting tubes such that air is sent to every cell in every tissue Book Lungs Spiders have book lungs, chambers with leaf-like plates for exchanging gases; air flows over the plates and blood flows through them Nervous system Arthropods have a well-developed nervous system that is of the same overall design as the annelids; anterior brain and a double, ventral hollow nerve cord. The sensory receptors of arthropods are usually associated with modifications of the chitinous exoskeleton The head usually bears various kinds of sense organs (e.g. antennae) with extreme sensitivity Nervous system They have a cerebral ganglion which forms a small, centralized brain which is connected to the ventral nerve cord, which runs the length of its body. At each segment, segmental ganglion branch off from the ventral nerve cord, thus connecting every segment to the arthropod to the brain. Each segmental ganglion must be well coordinated with each other since they must interact in order to control muscle contractions in each segment that are responsible for locomotion Nervous system cont. Many arthropods have compound eyes - eyes that are composed of many visual units called facets (ommatidia); capable of color vision and detecting slightest movements of prey or predators Some eyes are simple eyes with only a few photoreceptors; however, they are capable of forming crude images Digestive System Divided into 3 main regions: foregut, midgut, and hindgut Foregut and the hindgut are lined with chitin Foregut is involved with ingestion, mechanical breakdown, and storage Hindgut is involved with water absorption and formation of the feces Midgut is not lined with chitin; involved with digestion and absorption Outpockets (e.g. digestive glands) increase the surface area for digestion and absorption  Internal Transport and Excretion Open circulatory system Many crustaceans possess an excretory organ called the green gland (antennal gland), wh