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Kingdom – Animalia
Phylum – Chordata
Subphylum – Vertebrata


Include fish, amphibians, reptiles, birds, & mammals
Have a notochord (slim, flexible rod) present in early stages that may be replaced by backbone in adults
Contain a dorsal, hollow bundle of nerves called the nerve or spinal cord
Respire through pharyngeal or gill pouches during early development
Have post-anal tail in early stages
Endoskeleton made of bone &/or cartilage
Anterior head with well developed brain & sensory organs (Cephalization)
Closed circulatory system

Taxonomy of Vertebrates:

Agnatha include hagfish & lamprey with long, eel-like bodies without jaws or paired fins & cartilage skeletons

Chondrichthyes include sharks, rays, & skates with cartilage skeletons, paired fins, & jaws

Osteichthyes are bony fish with jaws, paired fins, & bone and cartilage in their skeletons
Amphibia include frogs, toads, & salamanders that go through an aquatic larval or tadpole stage
Reptilia include snakes, turtles, lizards, & alligators that live on land, are covered with scales, & lay a tough, protective amniote egg
Aves are birds covered with feathers, adapted for flying, & with hollow bones
Mammalia have hair or fur & females have mammary or milk-producing glands


Fossil record shows jawless fish without paired fins appeared first about 550 million years ago
Ostracoderm was a jawless, bottom-feeding ancestor to the agnathans (modern jawless fish)

Development of jaws & paired fins allowed better movement & increased ability to capture prey
Extinct acanthodians or spiny fish were first jawed fish with paired fins

Jaws probably developed from gill arches (bone that supports the pharynx)

Characteristics of  Fish:  

Streamlined body & muscular tail for swimming
Most with paired fins for maneuvering
Body covered with protective scales & mucus layer to reduce friction when swimming
Have less dense body tissues & store less dense lipids to help them float
Respire through gills
Most have a lateral line system or a row of sensory structures running down each side of the organism to detect changes in water temperature, pressure, current, etc.

Most with well-developed sense of sight & smell
Some can detect electrical currents
Ectotherms (adjust body temperature to environment)
Two chambered heart (upper atrium receives blood & lower ventricle pumps blood)

Agnatha (Jawless Fish):

Hagfish (live in oceans) & lampreys (found in marine & freshwater)
Circular mouths
Sharp teeth & strong rasp-like tongue to tear hole in prey & suck out blood & body fluids

Known as cyclostomes
Eel-shaped body
Mucus covers body
Skeleton made of cartilage
No paired fins
Gills without bony cover (called operculum)
Retain their notochord throughout their life
Hagfish are bottom dwellers in cold marine waters that burrow in mud, scavenge on dead & dying fish, & have tentacles around their mouth
Lampreys are usually parasites with a keen sense of smell to locate prey, lay their eggs in freshwater streams, & are covered with a poisonous slime


Includes sharks, rays, & skates
Endoskeleton of cartilage
Hinged jaws & paired fins
Placoid scales & tooth-like dermal spines on scales

Sharks are torpedo shaped

Rays & skates have broad, flat bodies with wing-like fins and a tail

Shark Characteristics:

Fast swimmers
Large, oily liver (20% of body weight) makes them buoyant
Tough, leathery skin
Fierce predators
Whale shark is largest & filter feeds on plankton

Ventral mouth with 6-20 rows of sharp, replaceable teeth
Short, straight intestine with spiral valve to slow food movement
5-7 pairs of gills for gas exchange
Kidneys remove wastes & maintain water balance
Electroreceptors on head help find prey & navigate
Lateral line along side of body contains sensory cells to detect vibrations & pressure
Separate sexes with external fertilization

Ray & Skate Characteristics:

Usually harmless to humans
Broad, wing-like pectoral fins used to glide through water
Flattened bodies with ventral mouth
Both eyes on top of head
Have protective coloration (darker on top & lighter on bottom)
Feed on fish & invertebrates
Stingray with poison spine by tip of tail

Electric ray gives off strong, electric shock
Manta ray is largest

Traits of Bony Fish (Osteichthyes)

Skeleton made of bone
Hinged jaws
Paired fins
Gills for gas exchange
Lateral line
Body covered with scales & mucus coating
Includes lobe-finned, ray-finned, and lung fish

Lobe-finned Fish:

Muscular, paddle-like fins supported by bone
Known as coelacanths

Thought to be extinct until 1938 when species found in Africa
Live in deep oceans


Use lungs & gills
Eel-shaped body

Live in shallow, tropical rivers of Africa, Australia, & South America
Come to surface & gulp air when oxygen level is low
Form mud cocoon & become dormant if stream dries up

Ray-finned Fish:

Fan-like fins supported by rays
Includes salmon, perch, catfish, tuna, etc.
Body covered with round, overlapping cycloid or ctenoid scales & mucus

Four sets of gills covered by bony operculum

Have movable fins
Dorsal fin(s) located on top keep fish upright & used for defense
Caudal fin or tail moves side to side to help steer
Pectoral fins (paired) on each side behind the operculum
Pelvic fins (paired) on ventral surface near the head
Anal fin (single) behind anus

Swim bladder is thin-walled sac in abdomen that creates buoyancy from diffusion of dissolved gas from blood


Kidneys filter the blood & help maintain water balance
Ectothermic – body temperature regulated by the environment
Keen sense of smell (nostrils) & have chemical receptors over the body
Can detect the earth’s magnetic field as a guide to navigate oceans
Have separate sexes with external fertilization
Eggs hatch into fry

Salmon Life Cycle:

Migrate up to 3200 kilometers following magnetic cues in the ocean
Follow mucus trails when navigating rivers
Return to birthplace to spawn
Males change color & jaw lengthens & develops a hook

Female uses her tail to build gravel nest & lays up to 10,000 eggs 
Male deposits sperm over eggs
Adults usually die after spawning
Pacific salmon return to sea when 15 cm long; while Atlantic salmon may stay in river up to 7 years
Secrete mucus coating in river as return to sea
May stay in ocean 6 months to 5 years