Phylum Chordata, subphylum Vertebrata

• Share the 4 chordate characters with lancelets and sea squirts

• Backbone, vertebral column, spine– Series of hollow vertebrae– Protects nerve cord

(spinal cord)

• Bilateral symmetry• endoskeleton

Agnatha (jawless fishes)• Lack: paired fins, scales,

& well developed vertebrae

• Hagfish (slime eels)– Mucus for protection– Feed on decaying flesh

• Lampreys– Parasitic– Anadromous

• Marine adults, breed in freshwater

Chondrichthyes (cartilagenous fishes)

• Sharks, rays, skates, & ratfishes

• Movable jaws of ventral mouth

• Paired fins• Placoid scales

– Dentricles (same composition as teeth)

Sharks• Heterocercal caudal fin• Two dorsal fins• Paired pectorals• 5-7 gill slits• Many rows of teeth• Oily liver • Diverse examples:

hammerhead, sawfish, thresher, whale sharks

Rays, Skates, & Ratfishes• Flattened• Demersal• 5 prd ventral gill slits• Expanded pectoralsRays vs. skates

rays: reduced or no dorsal fin

– Stingrays• Venomous defensive spine

– Electric rays• Upto 200 volts for defense and

predation– Ratfishes (chimaeras)

• Deep, bottoms, long skinny tail• Paired (pelvic) & unpaired

(forehead) male claspers for copulation & holding female--seen in rabbitfish

Osteichthyes (bony fishes)

• Swim bladder• Operculum (gill cover)• Homocercal tail• Scales of bony origin

– Smooth cycloid– Spiny ctenoid

• Diverse morphologies, habits, & behaviors

• Tear flesh; most swallow whole by: snout; protrusible; beak-like; large filtering mouths

• Undulating entire body; muscular caudal flex; fins only; caudal fin only

Digestive systems

• Mouth• Esophagus• Stomach• Intestine w/ increased SA

– spiral valve– pyloric caeca

• Pancreas– Digestive enzymes

• Liver– Bile to breakdown fats

• cloaca or anus

Circulatory system: 2 chambered heart (“one way flow”) …atrial chamber to gills, “fresh” blood to tissues, back to ventricle chamber

a.) Water across gills through mouth and spiracles in cartilagenous fishes

– Why are spiracles significant?b.) Opercula of bony fishes opens and

closes with mouth; greater suction; more efficient

Gill function and diffusion of gas• High surface area

from many folds or lamellae of gill filaments

• The water : blood relationship is in a counter-current orientation -- enhances diffusion– higher [Oxygen] in

water than blood

Osmosis

a.) concentrated urea prevents dehydration to deal with excess salts; excrete via rectal gland

b.) to compensate for tissue water loss: drink sea water, conserved by kidneys, excrete urine

Fish reproduction & development• Internal fertilization

– w/specialized copulatory structures

• External fertilization– Broadcast spawning

• Millions of eggs released as part of plankton

– Some fishes deposit eggs on bottoms– Some bury in sandy shores

• Unique examples: – Male carriers

• e.g. At Birch aquarium

• Oviparous– Eggs released, fertilized, developed

externally, lots of yolk• Viviparous

– Internal development, direct nourishment; birth live young

• Ovoviviparous– Internal egg development; yolk; birth

live young