Chapter 33 Invertebrates PDF

Chapter 33 An Introduction to Invertebrates  A Dragon Without a Backbone Invertebrates are animals that lack a b...

Chapter 33 An Introduction to Invertebrates  A Dragon Without a Backbone Invertebrates are animals that lack a backbone They account for more than 95% of known animal species Invertebrates are morphologically diverse and occupy almost every habitat on Earth ◦ For example, the blue dragon is a sea slug with finger-like structures that resemble the limbs of a dragon Mollusca, gastropoda, nudibranchia Eumetazoa = have tissues and two or three germ layers Ecdysozoa = shed outer layer to grow Lophotrochozoa/Spiralia = ciliated feeding structure Deuterostomia = Blastopore becomes the anus Porifera Cnidaria Eumetazoa Lophotrochozoa Bilateria Ecdysozoa Common ancestor of all animals Deuterostomia Current consensus animal phylogeny based on molecular and morphological data * All phyla have marine species. Only a subset also have terrestrial * or freshwater species. Spiralia/ * Animals evolved in the sea. * * * * * Big Nine Phyla indicated with * * Updated Animal Phylogeny Basal Metazoans Porifera Acoela Ctenophora (5,500 species) (400 species) (100 species) 1.5 mm A sponge Acoel flatworms Cnidaria Placozoa (1 species) (10,000 species) 0.5 mm comb jelly A jelly A placozoan Big Nine! Sponge Video Porifera (5,500 species) Azure vase sponge (Callyspongia plicifera) Sponges are basal animals that lack tissues. They are sedentary except for the larval stage. They live in marine and fresh water.  Food particles in mucus Choanocytes Collar Choanocyte Osculum Phagocytosis Flagellum of food particles Amoebocyte Pores Spicules Epidermis Water flow Amoebocytes Sponges lack tissues, groups of similar cells that act as functional units Sponges have several different cell types ◦ Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended food ◦ Sponges consist of a gelatinous noncellular mesohyl layer between two cell layers ◦ Amoebocytes are totipotent cells found in the mesohyl that play roles in digestion and manufacture of skeletal fibers Sponge larvae Most sponges are hermaphrodites: Each individual functions as both male and female (produces both eggs and sperm) Most exhibit sequential hermaphroditism: They function first as one sex and then as the other  Placozoa (3 genera) 0.5 mm Simple bilayer of a few thousand cells about 1 mm across No tissues DNA analysis places them as the most basal metazoan after sponges  Ctenophora (100 species) Diploblastic and radially symmetric Split from the animal lineage about the same time as cnidarians They move through the water using eight “combs” of cilia Comb jelly Big Nine! Cnidarians are an ancient phylum of eumetazoans Cnidaria (10,000 species) Jellies, corals, and hydras Diploblastic *mostly,* radial body plan Both sessile and motile forms Nerve net  Cnidarians are carnivores that use tentacles to capture prey The tentacles are armed with cnidocytes, unique cells that function in defense and capture of prey Nematocysts are specialized organelles within cnidocytes that eject a stinging thread Anemone feeding  Tentacle Cuticle of prey Thread Nematocyst “Trigger” Thread discharges Thread (coiled) Cnidocyte Two clades of Cnidarians Medusozoans Jellies Sea wasp Anthozoans Sea anemones Star corals  Scyphozoan Medusozoans Medusozoans include all cnidarians that produce a medusa ◦ Scyphozoans (jellies) ◦ Cubozoans (box jellies) ◦ Hydrozoans: mostly alternate between a medusa and polyp stage. Hydrozoan Portuguese Man o’ War box jelly There are two variations on the body plan: the sessile polyp and motile medusa A polyp adheres to the substrate by the aboral end of its body A medusa has a bell-shaped body with its mouth on the underside Medusae do not attach to the substrate but move freely The medusa is the predominant stage in the life cycle of most scyphozoans and cubozoans Medusozoans Mouth/anus Tentacle Gastrovascular cavity Gastrodermis Mesoglea Body stalk Epidermis Tentacle Mouth/anus Polyp (cross section) Medusa (cross section) Medusozoan life cycle Haploid (n) Diploid (2n) Reproductive polyp Medusa Feeding polyp Medusa MEIOSIS bud Gonad Egg Sperm SEXUAL ASEXUAL REPRODUCTION REPRODUCTION (BUDDING) Portion of FERTILIZATION a colony of polyps Zygote Developing polyp Planula (larva) Mature polyp 1 mm Anthozoans The clade Anthozoa includes the corals and sea anemones Anthozoans occur only as polyps Considered most like the ancestral Cnidarians Corals often form symbioses with algae and secrete a hard exoskeleton (external skeleton)  Acoela (400 species) Also called Xenacoelomorpha, they were once included with flatworms. Molecular evidence shows they are basal bilaterians No coelom, simple sac-like 1.5 mm gut Acoel flatworms  Spiralia/Lophotrochozoans A clade identified by molecular data (DNA) Widest range of animal body forms Bilaterian animals have bilateral symmetry and triploblastic development Most have a coelom and a digestive tract with two openings The clade Bilateria contains Spiralia/Lophotrochozoa, Ecdysozoa, and Deuterostomia Porifera Cnidaria Spiralia/ Lophotrochozoa Bilateria Ecdysozoa Deuterostomia Big Nine! Platyhelminthes: Flatworms Free-living members of phylum Platyhelminthes live in marine, freshwater, and damp terrestrial habitats Many flatworms are parasites, such as flukes and tapeworms Unlike most triploblastic animals, Platyhelminthes flatworms are acoelomates (animals (20,000 species) that lack a body cavity) Flatworms have a gastrovascular cavity with one opening The excretory apparatus consists of protonephridia, networks of ciliated tubules that pull fluid through ducts opening to the outside Flatworms have a dorsoventrally flattened to maximize the surface area across which gas exchange can occur Free-Living Species The best-known platyhelminthes are planarians Planarians live in fresh water and prey on smaller animals Planarians have light-sensitive eyespots and centralized nerve nets All the cells in a flatworm body are close to the gut and close to the water outside. No circulatory system, no gills. Pharynx Gastrovascular cavity Mouth Ventral nerve cords Eyespots Ganglia Parasitic Species Parasitic platyhelminthes live in or on other animals Two important groups of parasitic species are the trematodes and the tapeworms Parasites often lose some body features of their phylum during natural selection  Tapeworms are parasites of 100 µm vertebrates They do not have a mouth or gastrovascular cavity; instead, they absorb nutrients directly from the host’s intestine Hooks Sucker Fertilized eggs, produced by sexual reproduction, leave the Proglottids with host’s body in feces reproductive structures Scolex © 2017 Pearson Education, Inc. Lophophorates: Ectoprocts and Brachiopods Lophophorates have a lophophore, a crown of ciliated tentacles around their mouth used for feeding Lophophorates have a true coelom Lophophorates include two phyla: Ectoprocta and Brachiopoda Ectoprocta Brachiopoda (4,500 species) (335 species) Rotifers and Acanthocephalans Phylogenetic analyses have shown that rotifers (former phylum Rotifera) and acanthocephalans (former phylum Acanthocephala) should be combined into a single phylum, Syndermata Syndermata (2,900 species) Rotifers Rotifers are tiny animals that inhabit freshwater, marine, and damp soil habitats Rotifers are smaller than many protists but are truly multicellular and have specialized organ systems They are pseudocoelomates, and a gut with a mouth and anus Rotifers reproduce by parthenogenesis, in which females produce offspring from unfertilized eggs Some species are unusual in that they lack males entirely  Gastrotricha (800 species) “Hairy-belly” worms live on the bottom of the ocean or lakes feeding on Decayed organic matter 200 µm A gastrotrichan (differential- interference-contrast LM)  Cycliophora (1 species) This phylum was discovered in 1995. It lives on the mouthparts of lobsters 100 µm A cycliophoran (colorized SEM)  Nemertea (900 species) Lack a coelom, but have a gut. Have blood in vessels, but no heart. A ribbon worm  Annelids: segmented Big Nine! worms Annelids are coelomates with bodies composed of a series of fused rings Recent molecular analyses indicate that the annelids can be divided into two major clades ◦ Errantia Annelida ◦ Sedentaria (16,500 species) The phylum Annelida was traditionally divided into three clades ◦ Polychaeta (polychaetes) ◦ Oligochaeta (oligochaetes) ◦ Hirudinea (leeches) Errantians Most members of clade Errantia are mobile marine predators or grazers Many errantians have a pair of paddle-like or ridge-like structures called parapodia (“beside feet”) on each body segment Each parapodium has numerous chaetae, bristles made of chitin Parapodia are not unique to this clade  Sedentarians Sedentarians tend to be less mobile than errantians Some species burrow into the substrate, while others live in protective tubes Tube-dwelling sedentarians often have elaborate gills or tentacles used for filter feeding This clade also contains the leeches and the earthworms Leeches Most species of leeches live in fresh water; some are marine or terrestrial Leeches include predators of invertebrates and parasites that suck blood Some parasitic leeches slit the skin of their host and secrete an anesthetic to prevent detection They secrete another chemical called hirudin to prevent blood from coagulating Earthworms Earthworms eat through soil, extracting nutrients as the soil moves through the alimentary canal Earthworms are hermaphrodites but cross- fertilize Some reproduce asexually by fragmentation Video: Earthworm Locomotion Big Nine! Molluscs Mollusca Phylum Mollusca includes (100,000 species) snails and slugs, oysters and clams, and octopuses and squids Most molluscs are marine, though some inhabit fresh water and some snails and slugs are terrestrial Molluscs are soft-bodied animals, but most are protected by a calcium An octopus carbonate shell  Most molluscs have separate sexes with gonads located in the visceral mass, but many snails are hermaphrodites The life cycle of many molluscs includes a ciliated larval stage called a trochophore Sea snail trochophore larva Four of the major classes of molluscs are ◦ Polyplacophora (chitons) ◦ Gastropoda (snails and slugs) ◦ Bivalvia (clams, oysters, and other bivalves) ◦ Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses) Chitons Chitons are oval-shaped marine animals encased in an armor of eight dorsal plates They use their foot like a suction cup to grip rock, and their radula to scrape algae off the rock surface  About three-quarters of all living species of Gastropods molluscs are gastropods Most are marine, but there are many freshwater and terrestrial species Gastropods move slowly by a rippling motion of the foot or by cilia A land snail A sea slug Bivalves Bivalves are aquatic and include many species of clams, oysters, mussels, and scallops They have a shell divided into two halves drawn together by adductor muscles Some bivalves have eyes and sensory tentacles along the edge of their mantle Cephalopods Cephalopods are active marine predators with beak-like jaws surrounded by tentacles They are able to immobilize prey with a poison present in their saliva The foot is modified into a muscular excurrent siphon and part of the tentacles The shell is reduced and internal or missing in most species, except the chambered nautiluses  Squid Cephalopods Octopus Chambered nautilus  Octopus video Cephalopods have a closed circulatory system, well-developed sense organs, and a complex brain Some Cephalopods are intelligent and can learn Shelled cephalopods called ammonites were common but went extinct at the end of the Cretaceous period, 65.5 million years ago Ecdysozoans are the most species-rich animal group Ecdysozoans are covered by a tough coat called a cuticle The cuticle is shed or molted through a process called ecdysis The two largest phyla are nematodes and arthropods Porifera Cnidaria Spiralia/ Lophotrochozoa Ecdysozoa Deuterostomia  Loricifera (10 species) Tiny animals that live buried in sediment and eat bacteria 50 µm Lorica = “corset” A loriciferan (LM)  Priapula (16 species) Burrow in the sea floor sediments. Priapulans have been around since the Cambrian Named after the Greek God of fertility A priapulan  Onychophora (110 species) Velvet worms Originated in the sea, but now only live in humid forests No aquatic species known An onychophoran  Tardigrada (800 species) Water bears 100 µm Very small, most are less than 0.5 mm Can survive freezing and complete desiccation Tardigrades (colorized SEM) Big Nine! Nematodes: round worms Nematodes, or roundworms, are found in most aquatic habitats, in the soil, in moist tissues of plants, and in body fluids and tissues of animals They have an alimentary canal, but lack a circulatory system Body wall muscles are all Nematoda longitudinal, and their contraction (25,000 species) produces a thrashing motion Some species of nematodes are important parasites of plants and animals, but many are free-living in moist soil and aquatic habitats Trichinella spiralis is a parasite that can be acquired by humans from undercooked pork Caenorhabditis elegans is a soil nematode that has become a model research organism Video: C. elegans Embryo Development (Time Lapse) Video: C. elegans Crawling © 2017 PEARSON EDUCATION, INC. Big Nine! Arthropods Zoologists estimate that there are about a billion billion (1018) arthropods living on Earth More than 1 million species have been described, and two out of every three known species of animals are arthropods Members of the phylum Arthropoda Arthropoda are found in nearly all habitats of (1,000,000 species) the biosphere  Arthropod Origins The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages This body plan dates to the Cambrian explosion (535–525 million years ago) Early arthropods show little variation from segment to segment Arthropod evolution shows fusion and specialization of segments © 2017 PEARSON EDUCATION, INC. General Characteristics of Arthropods The appendages of some living arthropods are modified for functions such as walking, feeding, sensory reception, reproduction, and defense These modified appendages are jointed and come in pairs Crab feeding video The body of an arthropod is completely covered by the cuticle, an exoskeleton made of layers of protein and the polysaccharide chitin When an arthropod grows, it molts its exoskeleton Evolution of the exoskeleton in early arthropods enabled them to be among the first animals to colonize land ◦ Its relative impermeability to water helped prevent desiccation Morphological and molecular evidence suggests that living arthropods consist of three major lineages that diverged early in the phylum’s evolution ◦ Chelicerates (sea spiders, horseshoe crabs, scorpions, ticks, mites, and spiders) ◦ Myriapods (centipedes and millipedes) ◦ Pancrustaceans (lobsters and other crustaceans, as well as insects and their relatives) Chelicerates Chelicerates, clade Chelicerata, are named for clawlike feeding appendages called chelicerae The earliest chelicerates were eurypterids (water scorpions) Most marine chelicerates (including eurypterids) are extinct, but some species survive today, including horseshoe crabs Most modern 50 µm chelicerates are Scorpion arachnids, which include spiders, scorpions, ticks, and mites They have 8 legs, book lungs, and many Dust mite spiders produce silk Web-building spider Myriapods The clade Myriapoda includes millipedes and centipedes All living myriapods are terrestrial, but they first evolved in the sea They have a pair of antennae and three pairs of appendages modified as mouthparts Millipedes eat decaying leaves and plant matter Millipedes have many legs, with two pairs per trunk segment Myriapods Centipedes are carnivores Centipedes have one pair of legs per trunk segment Poison claws on the foremost trunk segment paralyze prey and aid in defense Pancrustaceans Recent evidence indicates that terrestrial insects are more closely related to crustaceans than myriapods Some lineages of crustaceans are more closely related to insects than other crustaceans Together, insects and crustaceans form the clade Pancrustacea Arthropods Insects Common ancestor Remipedians of arthropods (a crustacean group) Other crustaceans Myriapods Chelicerates Crustaceans Crustaceans (crabs, lobsters, shrimps, barnacles, and others) live in marine, freshwater, and terrestrial environments Many crustaceans have highly specialized appendages Small crustaceans exchange gases through the cuticle; larger crustaceans have gills Barnacles are a group of mostly sessile crustaceans They have a cuticle that is hardened into a calcium carbonate shell Insects Hexapoda is an enormous clade including insects and their relatives Insects live in almost every terrestrial habitat and in fresh water; flying insects fill the air They are rare in marine habitats The internal anatomy of an insect includes several complex organ systems Insects diversified rapidly following the evolution of flight 359–252 million years ago An animal that can fly can escape predators, find food, and disperse to new habitats much faster than organisms that can only crawl Insects evolved flight without sacrificing a pair of walking legs because wings are an extension of the cuticle Many insects undergo metamorphosis during their development Insects with complete metamorphosis have larval stages known by such names as maggot, grub, or caterpillar The larval stage looks entirely different from the adult stage Metamorphosis from larva to adult occurs during a pupal stage (a) Larva (b) Pupa (caterpillar) (c) Later-stage pupa (d) Emerging adult (e) Adult Video: Butterfly Emerging Archaeognatha (bristletails; 350 species) Zygentoma (silverfish; 450 species) Winged insects (many orders; six are shown below) Complete metamorphosis Incomplete metamorphosis Coleoptera: Beetles Hemiptera: Cicadas, 350,000 species) bugs (85,000 species) Diptera: Flies (151,000 species) Orthoptera: crickets+ (13,000 species) Hymenoptera: Bees, Ants (125,000 species) Proboscis Lepidoptera: Butterflies, Moths (120,000 species) Echinoderms and Chordates are Deuterostomes Echinoderms (phylum Echinodermata) include sea stars and sea urchins Vertebrates (animals that have a backbone) are members of phylum Chordata Echinoderms and chordates constitute the clade Deuterostomia Deuterostomes share developmental characteristics ◦ Radial cleavage ◦ Formation of the anus from the blastopore However, some other animals also share these developmental characteristics Deuterostomes are defined primarily by DNA similarities, rather than developmental similarities Porifera Cnidaria Spiralia/ Lophotrochozoa Ecdysozoa Deuterostomia  Hemichordata (85 species) Hemichordates are Deuterostomes with gill slits and a dorsal nerve cord Considered a sister group to echinoderms An acorn worm Big Nine! Chordates Phylum Chordata consists of two basal groups of invertebrates as well as vertebrates Chordates are bilaterally symmetrical coelomates with segmented bodies and a notochord Chordates did not evolve from echinoderms, but have evolved separately from them for at least 500 million years Chordata (57,000 species) Pikaia: oldest chordate A tunicate Big Nine! Echinoderms Sea stars and most other echinoderms are slow-moving or sessile marine animals A thin epidermis covers an endoskeleton of hard calcareous plates Echinoderms have a unique water vascular system, a network of hydraulic canals branching into tube feet that function in locomotion and feeding Males and females are usually separate, and sexual reproduction is external Echinodermata (7,000 species) Video: Echinoderm Tube Feet Most adult echinoderms appear to have radial symmetry with multiples of five Echinoderm larvae have bilateral symmetry Living echinoderms are divided into five clades ◦ Asteroidea (sea stars and sea daisies) ◦ Ophiuroidea (brittle stars) ◦ Echinoidea (sea urchins and sand dollars) ◦ Crinoidea (sea lilies and feather stars) basal lineage ◦ Holothuroidea (sea cucumbers) Asteroidea: Sea Stars and Sea Daisies Sea stars have multiple arms radiating from a central disk The undersurface of each arm bears tube feet, which grip a substrate with adhesive chemicals Sea stars feed on bivalves by prying them open with their tube feet, everting their stomach, and digesting their prey externally with digestive enzymes Sea stars can regrow lost arms Ophiuroidea: Brittle Stars Brittle stars have a distinct central disk and long, flexible arms that they use for movement Some species are suspension feeders, while others are predators or scavengers Echinoidea: Sea Urchins and Sand Dollars Sea urchins and sand dollars have no arms but have five rows of tube feet Sea urchins also use their spines for locomotion and protection Sea urchins feed on seaweed using a jaw-like structure on their underside Sea urchins are roughly symmetrical; sand dollars are flat disks Sand dollar video Crinoidea: Sea Lilies and Feather Stars Sea lilies live attached to the substrate by a stalk Feather stars can crawl using long, flexible arms Both use their arms in suspension feeding Crinoidea are the most basal echinoderms, and have changed little over the course of evolution Holothuroidea: Sea Cucumbers Sea cucumbers lack spines, have a very reduced endoskeleton, and do not look much like other echinoderms Sea cucumbers have five rows of tube feet; some of these are developed as feeding tentacles Sea cucumbers have lost the 5-part symmetry as adults that most echinoderms have Sister clade to Echinoidia  Phylum Description Porifera (sponges) Lack tissues; have choanocytes (collar cells—flagellated cells that ingest bacteria and tiny food particles) Cnidaria (hydras, jellies, sea Unique stinging structures (nematocysts) housed in anemones, corals) specialized cells (cnidocytes); diploblastic; radially symmetrical; gastrovascular cavity (digestive compartment with a single opening) Platyhelminthes (flatworms) Dorsoventrally flattened acoelomates; gastrovascular cavity or no digestive tract Syndermata (rotifers and Pseudocoelomates. Rotifers have alimentary canal acanthocephalans) (digestive tube with mouth and anus) and jaws (trophi); Lophotrochozoa acanthocephalans are parasites of vertebrates Lophophorates: Ectoprocta, Coelomates with lophophores (feeding structures Brachiopoda bearing ciliated tentacles) Mollusca (clams, snails, squids) Coelomates with three main body parts (muscular foot, visceral mass, mantle); coelom reduced; most have Metazoa hard shell made of calcium carbonate Annelida (segmented worms) Coelomates with segmented body wall and internal Eumetazoa organs (except digestive tract, which is unsegmented) Bilateria Nematoda (roundworms) Cylindrical pseudocoelomates with tapered ends; Deuterostomia Ecdysozoa no circulatory system; undergo ecdysis Arthropoda (spiders, centipedes, Coelomates with segmented body, jointed appendages, crustaceans, and insects) and exoskeleton made of protein and chitin Echinodermata (sea stars, Coelomates with bilaterally symmetrical larvae and sea urchins) five-part body organization as adults; unique water vascular system; endoskeleton Chordata (lancelets, tunicates, Coelomates with notochord; dorsal, hollow nerve cord; vertebrates) pharyngeal slits; post-anal tail (see Chapter 34)