Class Main Characteristics

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7 Vertebrate Classes



Main Characteristics



Jawless, cartilagenous skeleton, notocord present, lacks paires appendages, 2 chambered heart

Lamprey and Hagfish


Cartilagenous skeleton, jaws,paired appendages, gills, no operculum, no swim bladder, internal fertilization, placoid scales, 2 chambered heart.

Sharks, skates, rays, chimearas


Bony skeleton, jaws, external fertilization, swim bladder, operculum, ctenoid scales, 2 chambered heart.

Bass, trout, perch, tuna


Appendages adapted for land use,tadpole stage, respiration through lung/skin, smooth moist skin, 3 chambered heart.

Salamanders, newts, frogs, toads


Scaly skin, respiration via lungs, lay amniotic egg Partially divided septum.

Snakes, lizards, turtles, crocodiles


Feathers, forelimbs modified as wings, respiration though lungs, endothermic, 4 chambered heart, amniotic egg.

Owls, sparrow, penguins, eagles


young nourished by mammary glands, diaphragm, 4 chambered heart, hair, endothermic, viviparous

Monotremes, marsupials, and Placentals.

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Phylum Chordata


Chordate Characteristics:


  • Notochord. All chordate embryos have a notochord, which is a longitudinal, flexible rod of cartilage located between the gut and the dorsal nerve cord. The notochord may persist into adulthood in some chordates, but in many it is replaced by the vertebral column. The spongy material in between the vertebral bones is all that is left of the notochord.

  • Dorsal Hollow Nerve Cord. The nerve cord of a chordate embryo is formed from a plate of dorsal ectoderm that rolls up into a tube. It is located dorsal to the notochord. This nerve cord is unique due to its hollow structure. It will develop into the chordate's central nervous system .

  • Pharyngeal Gill slits. These structures are openings of the upper digestive tube in chordates. The pharynx is the area just behind the mouth. During the embryonic stage of the chordates these slits connect the outside to the pharynx. Early chordates used them as devices for filter feeding. As time progressed the slits became modified to function in gas exchange.

  • Post anal Tail. Most chordates have a tail extending beyond the anus. In many aquatic species the tail is equipped with skeletal and muscular tissue for movement.

Subphyla of Chordata:

Subphylum Cephalochordata. These invertebrate chordates contain all 4 phylum characteristics in their adult body. The lancelet Brachiostoma is the characteristic organism of this group. The animal wiggles into the sand , leaving its anterior end exposed. It pulls in water through its mouth and traps the food on the mucus of its pharyngeal gill slits. It has limited movement, using a (~) sinusoidal pattern.

Subphylum Urochordata. The common organisms are called tunicates. Most are sessile marine organisms. The organism has a body plan similar to that of a clam. Water is drawn into the body through an incurrent siphon; food particles are filtered out through the mucus covered gill slits. The food then moves into the intestine and the waste material is then passed out through the excurrent siphon. The adults lose 3 of the chordate characteristics as adults: Notochord, nerve chord , and tail.


Subphylum Vertebrata.

Cephalization, development of highly specialized sensory structures and a highly specialized brain.

Vertebral column, The axial skeleton ( skull, ribs, and vertebra ) and the appendicular skeleton ( arms and legs, or wings, or flippers ) is an internal living system.

Closed circulatory system. It is a closed system. The heart is composed of a collecting chamber(s) and a pumping chamber(s). The cells of the body exchange food and gases through tiny blood vessels called capillaries.

The kidney is the main excretory organ.

Sexes are separate. Fertilization may be internal or external depending on the species.

Respiratory organs include the gills, lungs, or highly vascularized skin. Oxygen is carried to all parts of the body in a liquid called blood. Hemoglobin is the main attractant of oxygen and is found in the red blood cells.



Main Characteristics



jawless, cartilage skeleton,gill slits, no swim bladder

Lamprey and Hagfish


Placoid scales, cartilage skeleton internal fertilization, paired fins,

Sharks, Rays, and Skates


Bony skeleton, paired fins, operculum, swim bladder

Tuna, Bass, Catfish, Flounder


Smooth skin, no claws, aquatic larvae, breathe through lungs and skin

Frog, Salamander, and Toad


Amniote egg, rough,dry skin, respiration through lungs

Snakes, Lizards, Turtles, and crocodiles


Feathers, amniote egg, extensive lung system, and wings



Hair, diaphragm, mammary glands, and bear live offspring.

Marsupials, monotremes, and Placentals

The Classes of Fish

Class Agnatha: (Lamprey and Hagfish)

General Characteristics:

  • Absence of jaws.

  • These organisms lack the paired fins (pelvic and pectoral).

  • Skeleton made of cartilage.

  • Round eel-like body with a compressed caudal fin.

  • Soft skin devoid of scales.

  • They lack a swim bladder and gill covers (operculum).

  • 7 gill slits on each side of the head.

  • The lamprey are parasitic and the hagfish are scavengers.

  • Ectothermic ( animals that cannot control their body temperature).

  • External fertilization. Oviparous ( egg laying)

  • Marine and fresh water species are found.

  • Lateral line

  • Two chambered heart

  • Gills used for respiration

  • No external ears

  • No eye lids


Class Chondrichthyes: ( Sharks, Rays, and Skates).

General Characteristics:

  • Skeleton made of cartilage.

  • Body covered with triangular Placoid scales.

  • Ventral,subterminal mouth with several rows of triangular teeth.

  • Large caudal fin with the dorsal section larger than the ventral one.

  • Paired fins ( pectoral and pelvic), are stiff and nonflexable.

  • They lack a swim bladder.

  • Ectothermic

  • Internal fertilization. Ovoviviparous ( developing egg kept inside the female for protection and does not live off of the parent).

  • Marine organisms only.

  • Lateral line

  • Two chambered heart

  • Gills used for respiration

  • No external ears

  • No eye lids


Class Osteichthyes: ( Tuna, Carp, Salmon, and Sturgeons).

General Characteristics:

  • Skeleton made of bone

  • Lateral line

  • Two chambered heart

  • Operculum covering the gills.

  • Swim bladder

  • Ectothermic

  • Paired fins made of rays and spines,or lobed fins lacking the rays and spines.

  • Various types of scales (ctenoid,ganoid, or cycloid).

  • Marine and fresh water species.

  • Gills used for respiration

  • External fertilization. Spawning. Oviparous.

  • No external ears

  • No eye lids.


Fish heart




Fish Circulation



Fish Brain


1. Olfactory Lobes : Functions in smell.

2. Cerebrum : Functions in muscle movement, intelligence, instinct, and will power.

3. Optic Lobes : Functions in eye sight.

4. Cerebellum : Functions in muscular coordination.

5. Medulla Oblongata : Functions in involuntary responses ( heart beat, breathing, and digestion ).

6. Spinal Cord : Functions in transport of nerve impulses to and from the brain.

Class Amphibia:


  • Amphibians have smooth moist skin. The toad is an exception with rough dry skin.

  • The majority of amphibians contain four limbs with no claws on their digits (toes).

  • They contain a three chambered heart. Two atria and one ventricle. There is a possibility of the oxygenated and unoxygenated blood mixing in the ventricle.

  • They are ectotherms. During extreme environmental conditions they either hibernate (winter) or aestivate (summer).

  • They carry on external fertilization. Their offspring develop through a process called metamorphosis. Tadpoles (aquatic larvae) resemble fish. Over a period of time they change in form into the adult amphibian.

  • They respire through poorly developed lungs and moist skin.

  • They contain a well developed muscular system.

  • The digestive system is adapted to digest whole prey, swallowed by the organism.

  • Two kidney's rid the body of nitrogenous waste. The amphibian liver carries on several functions: detoxifying poisons, producing bile, and storing glucose in the form of glycogen.

  • The cloaca is a sac that collects discharge from the large intestine, urinary bladder, and gonads before it is eliminated from the body.

  • Their brain is well developed and is attached to a dorsal nerve cord.

  • Most amphibians contain three eye lids. Two are normal and one is transparent.

  • These are the first animals to possess a pressure releasing canal called the Eustachian tube. The tube connects the mouth cavity with the tympanic membrane.


Orders of Amphibia:


Order Apoda. This order contains amphibians without legs. Examples of this order are the caecilians. Most of these organisms live in the moist soil, while some tropical species live in ponds and streams.


Order Urodela. These are tailed amphibians. Included in this group are the salamanders and newts. These animals contain a tail and neck. Some of these organisms never develop lungs and must rely on external gills.


Order Anura. Frogs and toads represent these tailless organisms. Frogs use powerful hind legs for movement. Their long sticky tongue is attached to the tip of the lower jaw. They exhibit a variety of colorful skin, which is sometimes poisonous. Frogs live in many areas of the world. The male is the only one of the species that makes sounds.


Tadpole and Adult Comparison


Adult Frog


Type of limbs



Heart chambers



Type of food



Respiratory structure

Lungs and Skin




Reptilian Characteristics:


  • The development of the amniote egg. Reptiles are considered the first true land animals. It was this egg that allowed the reptiles to conquer the land and begin a reign that lasted hundreds of millions of years. The amniote egg is a water proof structure composed of a shell, embryonic membranes, and the living embryo. Starting after the shell, the first extraembryonic membrane is the chorion. The chorion aids in the exchange of gases between the environment and the embryo. The allantois is a sac-like structure that grows out of the digestive tract of the embryo. It functions in gas exchange and collects metabolic wastes from the embryo. The third membrane is a fluid filled sac called the amnion. It surrounds the embryo and the fluid it secretes cushions the embryo. The fourth and final membrane is the yolk sac. The sac contains the food for the embryo.






  • A thick dry skin covered with scales made of a protein called Keratin. Reptiles molt as they grow.

  • Reproduction is sexual with internal fertilization. Most are oviparous, while some snakes and lizards are either ovoviviparous or viviparous.

  • Respiration occurs through well developed lungs, and in some turtles a moist cloacal surface.

  • Reptiles are ectotherms. Being ectothermic enables an organism to survive on much less food than an endothermic organism.

  • Most reptiles contain a 3 chambered heart with a partially divided ventricle. Crocodiles contain a 4 chambered heart.

Reptilian Orders.

  • Order Chelonia. Turtles are members of this order. They developed from animals called anapsids during the Mesozoic era. They show very little change from their ancestral form. They contain 2 shells. The top shell is called the carapace, while the lower shell is called the plastron. Both shells are colored to help the turtle blend in with the 2 environments in which it lives. All turtles lay their eggs on land. Turtles do not contain teeth, but use a horny beak to grab and tear food. Turtles contain three eyelids.

  • Order Squamata. Lizards and snakes belong to this reptilian order. Lizards are the most abundant of this order. They evolved from the diapsid group of primitive organisms. They range in size from the large Komodo Dragon to the small tropical geckos. Snakes are probably the most interesting species of this group. They probably developed from small burrowing lizards. They are void of legs, eyelids, and ears. They are carnivores swallowing their prey whole. Their glottis and gullet are at separate ends of the mouth cavity. This allows the snake to breathe when eating. They contain 2 rows of teeth on the upper jaw and one row on the lower. The teeth are curved and pointed back toward the gullet. This keeps the food moving in one direction toward the stomach. The jaws are hinged in such a way as to separate allowing the mouth to open wider than usual when swallowing large prey. Some species are venomous, either giving off a hemotoxin ( blood poison) or a neurotoxin ( nerve poison). The tongue is used in the sense of smell. Heat sensitive pits are a feature of some venomous snakes, these allows the snake to home in on the prey's body heat.

  • Order Crocodilia. Crocodiles evolved from the diapsid lineage. These organism are found in most of the warm regions of the world. They spend most of their time in the water. They contain a 4 chambered heart and are the closest living relative of the dinosaur.

Class Aves

General Characteristics:

  • Birds are flight orientated organisms. Each part of its anatomy is modified in some way to allow it to keep its body light and energetic for flight.

  • Very active metabolism. They can eat, digest, and eliminate the waste in a short amount of time. Their body temperature is rather high 102-103 degrees F. They are endotherms.

  • They contain a four chambered heart.

  • Their skeleton is constructed of light weight bones supported by an inner meshwork of bony material to give extra support while flying.

  • The female loses one of its ovaries.

  • They have no teeth and their beak is made of a light protein keratin.

  • They contain feathers, also made of keratin. There are three types of feathers: down feathers which are used for insulation, contour feathers which are colorful and used for recognition, and keeping the body aerodynamic, and quill feathers which are used for flight . These feathers are lost periodically (molting).

  • They have an extensive air sac system attached to the lungs. This reduces the weight of the bird and supplies the needed air for a fast metabolism. It also is used to dissipate the tremendous amount of heat built up from metabolism.

  • They develop from the amniote egg. Bird egg shells are hardened with calcium carbonate for added protection.

  • Birds that are ready to carry on life's duties upon hatching are called precotial, while those that need further development are called altricial.

  • They have a well developed nervous system. Acute vision, and external ears.

  • Well developed muscles. The keel ,a part of the sternum, allows large pectoral muscles to be attached to the skeleton.

  • Their forelimbs are modifies as wings. These wings are homologous to the limbs of the reptiles, amphibians, and mammals.

  • Their hind limbs are modified for various jobs based on the structure of their claws.

  • Birds are an excellent indicator of the fitness of the environment. They help keep the insect population down, use rodents as a food source, help rid the environment of dead and decaying organic material, and help pollinate many types of plants.

  • Many birds migrate over long distances to find suitable breeding grounds and protection from major climatic changes.

Class Mammalia

General Mammalian Characteristics:

  • Possess hair which is made of keratin. The evolution of mammalian keratin is believed to be independent of reptilian keratin. Hair provides insulation .

  • Endothermic. The majority of the heat energy is used to maintain their high body temperature.

  • 4 chambered heart.

  • Mammary glands are used to produce milk to nourish their young. Female glands are the only functional glands.

  • The diaphragm is a muscle that separates the thoracic cavity from the abdominal cavity.

  • 7 cervical vertebrae (neck bones) are present in most mammals.

  • Most are viviparous though some are oviparous. An extended gestation period (uterine development) is common in most placental mammals.

  • Teeth are imbedded in the jaw bone and come in a variety of forms.

  • Well developed brain.

  • Mammals developed from the therapsid ancestors during the Triassic period.

Major Groups of Mammals:

  • Monotremes. Characterized by the duckbilled platypus and the spiny anteaters, lay eggs and maintain some reptilian characteristics. They do not contain true mammary glands, but produce a fatty sweat (milk) from glands in the skin. The milk collects and drips down tufts of hair into the offspring's mouth. They are found in Australia and New Guinea.

  • Marsupials. These mammals contain a pouch (marsupium). Opossums,koalas,kangaroos, and other examples live in Australia as a result of the break up of the super continent Pangea. The young are born during the early stages of development. The new born crawls up to the mother's pouch, where it clings on to a nipple and hangs there until it fully develops.

  • Placental Mammals. These mammals are the most abundant and diverse of the class. The placenta, a reproductive structure, is housed in the uterus of the female. Here the offspring receives all that it needs to develop into a fully developed organism. This period of development (gestation) varies with the species of mammal. Whales gestate for 2 years, while a mouse develops in 21 days.

Chart of Placental Mammals





Eats meat, all teeth are pointed

cats and dogs , seals, walrus, weasels, and martins


wings used for flight, diet includes insects and vegetation



opposable thumb, plantigrade foot, usually one offspring at birth.

man , apes, monkeys,tarsiers,and lemurs


lacking teeth, large claws for digging

sloths, armadillos, South American anteater


2 incisors on both jaws, diastema between incisors and premolars

rats, mice, squirrels, beavers, gophers, and capybara


4 incisor teeth, canine teeth lacking, short stubby tails

rabbits, hares,pikas


flippers, opening on top of head



Great size,nose and upper lip form proboscis, upper incisors are tusks,thick skin,scant hair



Herbivorous, aquatic, no external ears, flippers, no hind appendages

Manatees and dugongs


Odd-toed,hoofed forms,gall bladder lacking, herbivorous

horses, donkeys,zebras,tapirs


Even-toed, hoofed forms, herbivorous, true horns or antlers present


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