Vertebrate Zoology - ZOO 117 PDF

ZOO 117: INTRODUCTORY VERTEBRATE ZOOLOGY TOPIC: CHARACTERISTICS AND CLASSIFICATION OF VERTEBRATES BY PROF. ADIAHA A. A. UGWUMBA  Vertebrates are the only chordates with backbones they are one of the three sub-phyla of chordates...

ZOO 117: INTRODUCTORY VERTEBRATE ZOOLOGY TOPIC: CHARACTERISTICS AND CLASSIFICATION OF VERTEBRATES BY PROF. ADIAHA A. A. UGWUMBA  Vertebrates are the only chordates with backbones they are one of the three sub-phyla of chordates the other two chordate sub-phyla are invertebrates, so they lack backbones  Phylum: Chordata Sub-phylum: Urochordata – sea squirts or tunicates Sub-phylum: Cephalochordata (= Acraniata)- lancelets Sub-phylum: Vertebrata (= Craniata) - vertebrates  Tunicates and lancelets are the invertebrate chordates  The only vertebrates in the entire Animal Kingdom belong to just one Sub-phylum - Vertebrata  SUB-PHYLUM: VERTEBRATA (CRANIATA) Common name: Vertebrates  Features: CEPHALIZATION is a prominent features of vertebrates because they all have a well-developed head They are metameric They all have endoskeleton They have a VERTEBRAL COLUMN, called VERTEBRAE which supports the trunk This is a series of metamerically arranged internal pieces of cartilaginous of bony skeleton which either surrounds or replaces the notochord in the adults.  Features of Vertebrates Contd. Anterior part of the nerve cord is enlarged to form a BRAIN which is a specialised complex structure Enclosing the brain is a brain case called CRANIUM OR SKULL with the following functions: protection of the brain and orbits of the eyes for muscle attachment (of the scalp and face) responsible for movement of head and facial expressions e.g frown helps to attach the brain and other head organs to the rest of the body by connecting to the spinal cord it holds the teeth in place together with facial bones, it protects and supports the sense organs Associated with the brain are special sense organs called receptors e.g. eyes, ears, nose, tongue etc.  Features of Vertebrates Contd. The pharynx in most vertebrates is small and the gill slits are few in number and often absent in adults – gill slits are only used for respiration (not also for feeding like in other chordates) They have CHAMBERED HEART for rapid blood circulation Circulatory system is closed, so they have distinct blood vessels There is the pigment, HAEMOGLOBIN in the red blood corpuscles to carry large amount of oxygen  Features of Vertebrates Contd. Excretory organs are KIDNEYS, which do not only remove wastes but also help to regulate the internal environment Endostyle (an organ used to filter food) is present in ammocoete larva of lampreys and it is transformed into thyroid gland in all other vertebrates They usually have two pairs of limbs Sexes are mostly separate, fertilization may be external or internal and development may be direct or indirect through a larval stage  CLASSIFICATION OF VERTEBRATES  There are two super classes of vertebrates: Superclass: Agnatha (the jawless fishes or jawless vertebrates) Superclass: Gnathostomata (jawed vertebrates) There are six classes of jawed vertebrates Class Chondrichthyes (cartilaginous fishes) Class Osteichthyes (bony fishes) Class Amphibia (amphibians) Class Reptilia (reptiles) Class Aves (birds) Class Mammalia (mammals)  TOPIC: CHARACTERISTICS AND LIFE HISTORY OF FISHES Jawless Fishes Cartilaginous Fishes Bony Fishes  SUPERCLASS: AGNATHA Common name: Jawless fishes or Jawless vertebrates e.g. Lamprey and Hagfish  Features: They are the most primitive vertebrates Many agnathans are extinct They do not have jaws True teeth are absent Their body is elongated and eel-like in shape  Features of Agnathans Contd. Living agnathans do not have scales; skin is slimy Adults are parasitic and marine while their larvae are free- living filter feeders on plankton, algae and detritus; and they live in freshwater. However, hagfishes are exclusively marine -The mouth of adult lamprey is circular and modified into a sucker armed with horny teeth and hooks for attachment to their host and also sucking of blood -Hagfish has tentacles round the mouth to detect their food and a tongue-like structure with hooks to capture their prey and suck fluids from dead remains or dying animals at the bottom of the sea Features of Agnatha Contd. They do not have paired appendages - they have fins which are not in pairs They have a single median nostril which leads to a single median olfactory organ Their skeleton is cartilaginous The embryonic notochord persists in the adult Gills are not protected or supported by gill arch Seven or more paired gill pouches are present The heart has two chambers  Features of Agnatha contd. Kidneys are adapted not only for excretion but also to regulate salt balance in both fresh and marine waters Most of them are hermaphrodites Fertilization is external and development is indirect through a larval stage called AMMOCOETE LARVA In lampreys, the larva is found in freshwater and it is a free-living filter feeder on plankton, while the adults are found in marine environment and they are parasitic on blood of other fishes or other vertebrates or worms Most of their 7-year live span is spent as larva (5-6 years) - adults die once they reproduce  Classification of Agnatha There are two classes of living agnathans Class: Petromyzontia (=Cephalaspidomorphi) – lampreys Family: Petromyzonidae e.g. Petromyzon sp. Class: Myxinoidea (hagfish) Family: Myxinidae e.g. Myxine sp. These two classes were formally grouped as one class namely Cyclostomata (lampreys and hagfishes) before they were separated  (seven pairs) Petromyzon (lamprey-adult) Mouth/Sucker of adult lamprey socratic.org showing hooks for attachment  Dorsal fin Caudal fin (used to detect Food) Myxine (hagfish - adult) Mouth of adult hagfish showing tentacles and newscientist.com tongue-like structure  Life History of Lamprey – a representative agnathan Many lampreys are anadromous; the adults migrate up rivers ie. freshwater to spawn During spawning, the lampreys stop eating, conserving all their energy for reproduction A nest is dug by a pair of male and female lampreys at the bottom in sand and gravel where eggs are laid, the males release their sperms and fertilization is external After spawning, the adults die because their intestines deteriorate and their bodies are attacked by fungi Eggs hatch into Ammocoete larva  Life History of Lamprey Contd. The larva has no teeth, they are blind and they have little resemblance to the adult Ammocoete Larva of Lamprey – lateral view  Life History of Lamprey Contd. The larvae drift downstream with the current till they reach soft and fine sediment in silt beds, where they burrow in silt, mud and detritus and become filter feeders The larva lives for about five to six years, before they undergo transformation (not eating during this period) - they then migrate to the sea, develop into adults and become parasitic The adults do not live long unlike the larvae The ammocoete larva has a low tolerance for high water temperatures, this is why agnathans are not distributed in the tropics  SUPERCLASS: GNATHOSTOMATA Common name: Jawed vertebrates  Features: They have jaws They have paired nostrils and paired olfactory organs Notochord is not complete, only traces always present They have paired limbs (legs or fins); though limbs may be secondarily lost in some e.g. snakes  Features of Gnathostomata Contd. Circulatory system is well developed: - There is a ventral heart and usually with at least three chambers Generally, blood is carried by arteries from the heart to various parts of the body and returned back to the heart by veins In most gnathostomes, lymph vessels are also present that return fluid from tissues to the heart  Features of Gnathostomata Contd. Respiratory system is made of gills, lungs or the skin Gill slits are generally present in the embryo though some members also have them in their adults Associated with gill slits are internal gills In higher gnathostomes, gills are replaced by lung, though gills are present in the embryos  CLASS: CHONDRICHTHYES Common name: Cartilaginous fishes e.g sharks, rays and skates, sawfishes, chimaeras  Features Their skeleton is made of cartilage Their caudal fin is heterocercal ie. asymmetrical They do not have operculum ie gill cover, so their gill slits are exposed, being external They have odontoid or placoid scales which are tiny and tooth-like or spine-like A placoid scale  Classification of Class: Chondrichthyes  There are two subclasses in this class SUBCLASS: ELASMOBRANCHII These are the sharks, rays, skates and sawfish (the last three are called batoid fishes) They are the common cartilaginous fishes SUBCLASS: HOLOCEPHALI Chimaeras are the only living holocephalian cartilaginous fishes and they are not common They are believed to be going into extinction  SUBCLASS: ELASMOBRANCHII Common names: sharks and batoid fishes (rays, skates and sawfishes)  Features They are usually marine Their skeleton is made of cartilage and not bone Sharks generally have a streamlined (fish-like) body, while the bodies of rays and skates are shaped like a bell; an anterior broad disc and a posterior tail Sawfish, also called carpenter shark is a family of rays characterized by streamlined body with a long, narrow, flattened extension of the snout called ROSTRUM which is lined with sharp transverse teeth, arranged such that it looks like a saw  Features of Elasmobranchii Contd. Paired fins are pectoral and pelvic fins In sharks, the front margin of the pectoral fins are free while in batoid fishes, pectoral fins are not free but continuous with the head In sharks, gill slits are lateral because they lie at the sides of the head; while in batoid fishes, the gill slits are ventral (ie. underneath) the head  Features of Elasmobranchii Contd. They also have modified gill slits on the dorsal surface called SPIRACLES, one behind each eye - the spiracles are more pronounced (very large) in rays and skates than in sharks They do not have operculum i.e. gill cover, so gill slits are external Caudal fin is heterocercal (i.e. it is asymmetrical) They have placoid (odontoid) scales They have mucus glands in skin  Features of Elasmobranchii Contd. Since they do not have bone and so no bone marrow, red blood cells are produced in the: - spleen -epigonal organ (special tissues surrounding the gonads) and -Leydig’s organ (located near the oesophagus)  Features of Elasmobranchii Contd. The inner margin of each pelvic fin in the male fish is grooved to form a CLASPER for the transmission of sperm into the female Sexes are separate. Fertilization is internal Development is usually direct by live birth (ovoviviparous or viviparous) Some are oviparous (egg laying)  Example of Sharks Order: Carchariniformis (Ground sharks) Family: Carcharinidae (Requin sharks) e.g. Carcharhinus sp. Scoliodon sp. Order: Squaliformes (Dogfish sharks) Family: Squalidae e.g. Squalus sp. Order: Sphyrniformes (Hammerhead sharks) Family: Sphyrnidae e.g. Sphyrna sp. Scoliodon sp. (shark) - lateral view Sphyrna sp. (Hammerhead Shark) – lateral view Modified from: www.exploringnature.org  Examples of Batoid Fishes Superorder: Batoidea Order: Myliobatiformes (rays) Family: Dasyatidae (Whiptail stingrays) e.g. Dasyatis sp. Order: Rajiformes (skates) Family: Rajidae e.g. Raja sp. Order: Pristiformes (Sawfishes) Family: Pristidae (Largemouth sawfish) e.g. Pristis sp. Dasyatis sp. (Sting ray) – dorsal view Snout Raja sp. (a skate) – dorsal view (Rostrum) Pristis sp. (Sawfish) - dorsal view Modified after Last and Stevens (1994) ZOO 117: INTRODUCTORY VERTEBRATE ZOOLOGY TOPIC: LIFE HISTORY OF ELASMOBRANCHII CHARACTERISTICS AND CLASSIFICATION OF OSTEICHTHYES LIFE HISTORY OF OSTEICHTHYES BY PROF. ADIAHA A. A. UGWUMBA  Life History of Shark – a representative Elasmobranch All sharks reproduce through internal fertilization The male shark does not have a penis but uses its claspers to insert into the female shark and transfers sperms to the eggs Fertilization is therefore internal Female sharks can store male sperm in order to fertilize their eggs later, if the time isn’t right for reproduction  Life History of Sharks Contd. There are 3 different ways that a baby shark can be born once a female shark has a fertilized egg, depending on the species 1. Viviparity: is when a shark nourishes her growing shark embryo internally through a placenta and gives birth to a fully-functional young alive eg. hammerhead sharks, requiem sharks 2. Ovoviviparity: in this case, there is no placenta linking the embryo to the female shark – the egg hatches while still inside the mother. Once hatched, the embryo gains nutrients from reserved food in the egg yolk, nutritious fluids from the mother’s womb, and sometimes from consuming other eggs in the uterus and are born as miniature adults – most sharks are ovoviviparous e.g whale shark  Life History of Sharks Contd. 3. Oviparous: a protective egg case is released and attached to rock or other hard surface at the bottom – the developing embryo inside the egg case gains nutrients from the yolk; once the nutrients from the yolk sac are used up, the small shark emerges out of the case to fend for itself eg. bamboo shark, carpet shark, horn shark, zebra shark Sharks do not care for their young, so they give birth to a small number of highly developed young ones alive and the new-born sharks care for themselves Sharks grow and mature slowly and reproduce only a small number of young in their lifetimes Female sharks, isolated from males can undergo internal asexual reproduction by parthenogenesis and produce young shark. The egg is fertilized by an adjacent cell known as a polar body. Zebra and hammerhead sharks are known to undergo parthenogenesis  CLASS OSTEICHTHYES Common name: Bony fishes  Features: They are found in all types of water bodies and they are presently the most abundant fishes They have streamlined body shape – elongated body - an adaptation for easy swimming Their skeleton is almost entirely made of bones Endoskeleton is reduced, so they are light - an adaptation for buoyancy in water (ie. ability to float) They have different types of scales e.g. cycloid (smooth edges), ctenoid (spinous posterior) and ganoid or rhomboid (diamond- shape) scales  Features of Osteichthyes Contd. Some bony fishes lack scales e.g. catfish Swim bladder is usually present - it is filled with gas (or fat in some species) - it is an adaptation for buoyancy Mouth has many teeth (some are toothless) eg. pipefish, seahorse Gills are supported by bony gill arch Operculum covers the gills Skin has mucus glands Tail is homocercal (symmetrical) They are mostly oviparous  Classification of Osteichthyes  There are three subclasses 1. Subclass Dipnoi – lungfishes -They are the group of fishes that led to amphibians -They are sometimes grouped in the Subclass Sarcopterygii -They have both gills and lung for respiration. - the lung is a modification of the swim bladder -They are eel-like in shape -Paired fins are modified into leg-like appendages used for walking on mud Order: Lepidosireniformes - Family: Protopteridae Operculum Protopterus sp. – African Lungfish  Classification of Osteichthyes Contd. 2. Subclass: Sarcopterygii (= Crossopterygii) Common name: lobe-finned fishes Fins are fleshy and lobe-shaped They are primitive bony fishes and most of them are extinct They have primitive scales called cosmoid scale which evolved from placoid scales  Example of Sarcopterygii There are only two living species, all in one order, family and genus Order: Coelacanthiformes (coelacanths) Family: Latimeriidae e.g. Latimeria sp. Latimeria sp. ( a coelacanth)  Classification of Osteichthyes Contd. 3. Subclass: Actinopterygii Common name: Ray-finned fishes This is the subclass of modern bony fishes This class contains the dominant types of fishes and they are the masters of the waters Their fins have rays Stream-line body is very pronounce Endoskeleton is highly reduced i.e an adaptation for buoyancy Examples of Ray-finned Fishes Order: Perciformes (perch) Family: Cichlidae (largely tilapias) e.g. Oreochromis sp. Order: Siluriformes (includes catfishes) Family: Clariidae (mud catfishes) e.g. Clarias sp. Oreochromis sp. ( a tilapia) Clarias sp. (mud catfish) - drawing  Life History of Bony fishes – representative Osteichthyes  Reproduction is generally cyclic in bony fishes, being regularly repeated The duration of cycles may be as short as four weeks or as long as many years Pacific salmon, Oncorhynchus sp., reproduces only once during its five-year life span, then dies soon after In many bony fishes, reproductive cycle is annual, breeding once a year, so they are annual spawners e.g. mud catfish like Clarias sp. while many others have multiple reproductive cycles breeding more than once a year, so they are multiple spawners e.g. in tilapias  Life History of Bony Fishes Contd. Fishes are generally oviparous Eggs are laid and fertilization is external Development is indirect through larval stages which are mostly planktonic and usually do not look like their adults See Developing stages of the Nile tilapia, Oreochromis below: Larval stages still carrying yolk Sac  Life History of Bony Fishes Contd. Some fishes shed their eggs in water and the males release sperm on the eggs as the females shed the eggs; fertilization occur in the water column Fishes that do not care for their eggs and young, lay large numbers of small eggs (millions) e.g. sardines - this is an adaptation for survival since a lot of such eggs are lost to predation, harsh environmental conditions etc. Some other fishes that protect or guard their eggs and young, lay few large eggs usually in a nest they build -the females lay the eggs (a few thousand or hundreds or less) in the nest and the males release sperm on them e.g. the red belly tilapia, Coptodon Life History of Bony fishes Contd. Some fishes are mouth brooders, they carry the eggs after fertilization and even the larvae after hatching in their mouth where they are incubated e.g. Nile tilapia Some fishes are ovoviviparous eg. Seahorse - eggs are deposited by the female in a pouch in the abdomen of the male where the male releases sperm to fertilize the eggs and they are incubated in the pouch - the embryos develop within the pouch from nutrients in the yolk sacs until the male gives birth to tiny sea horses  Life History of Bony fishes Contd. Some bony fishes are viviparous eg. Surf perches The females store sperms in the body until their ova are mature Fertilization is internal and the eggs are incubated inside the females and the developing embryo is nourished by connections to the mother - the embryo hatch inside the female’s body; the young fish is born alive