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 pectorals Rays 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