THE FIRST VERTEBRATES

Oldest and simplest vertebrates Most abundant vertebrates Three groups of fishes

◦ Jawless fishes◦ Cartilaginous fishes (Chondrichthyes)◦ Bony fishes (Osteichthyes)

◦ Yes, it is FISHES- the rule is fish is for a single individual or more than one individual of the same species

◦ FISHES- refers to more than one species

Class Agnatha Around 30 known species Includes hagfish & lampreys Feed by suction with aid from teeth No fins, & lack true vertebrae; no scales Body is elongated and cylindrical Most primitive fishes

Class Chondrichthyes Skeleton made of cartilage Movable jaws

◦ Mouth ventral Underneath the head Paired lateral fins Sandpaper-like skin because of Placoid

Scales Includes sharks, rays, skates, and ratfishes

◦ ~350 living species Caudal Fin is Heterocercal

◦ Upper lobe longer than lower lobe ◦ Fusiform, or spindle-shaped bodies ◦ Five to seven gill slits

Powerful jaws with rows of teeth that are Continuously replaced

◦ Carnivores & Filter Feeders◦ Found most often in warm

coastal waterMost only live in marine env.Some travel upstream

◦ ~450-500 known species ◦ Dorsoventrally flattened ◦ Demersal: fish that live on the bottom ◦ Five ventral gill slits

Stingrays Whip-like tail with stinging spines

Electric Rays Electric organs on each side of head

◦ Skates lack the stinging tail

◦ Ratfish: AKA Chimaeras ◦ ~30 known species ◦ Only one pair of gill slits covered by a flap of

skin ◦ Long, rat-like tail

www.itsallaboutfish.co.uk/ratfish.htm

Class Osteichthyes ~23,000 known species Skeleton made of bone Cycloid or Ctenoid Scales Operculum: Gill Cover Upper & lower tail fin same size:

Homocercal

Homocercal tail Cycloid scales

Fin Rays: thin membranes supported by bony spine

Anterior, terminal mouth More flexible jaws with teeth attached to

jawbone Swim Bladder: gas-filled sac above

stomach & intestines that helps in buoyancy

ICHTHYOLOGY- study of fish Body shape varies with habitat and lifestyle

◦ Fast swimmers are streamlined- like tuna, marlins, mackerels, sharks

Dorsoventrally flat- skates, rays and sea moths- demersal fish (live near bottom)

Dragon sea moth

Image from Liveaquaria.com

Laterally flattened bottom dweller fish such as flounder, halibut and sole

Born with eyes on both sides of body but as they mature, one eye migrates to the dominant side

Elongated bodies such as eels- live in narrow places amongst rock and coral reef

Laterally compressed bodies live around coral reefs, kelp beds etc.

Butterfly fish

snappers

CHROMATOPHORES-skin cells that contain pigments; irregular in shape with branches radiating out from the center of the cell

STRUCTURAL COLORS-Colors that result when light is reflected by a particular surface◦ Many times caused by IRIDOPHORES-

chromatophores with light-reflecting crystals

Colors reflect mood◦ warning coloration- coloration that allows

organisms to escape from predators by advertising something harmful or distasteful video

◦ cryptic coloration-color pattern that allows an organism to blend in its surroundings- video

◦ Disruptive coloration- a color pattern that helps break the outline of an organism

Ornate cowfishDisruptive coloration

COUNTERSHADING- a color pattern that results in a dark back and a light belly- most common in epipelagic fishes (surface to 200 m)