Chordates and Vertebrates

Chordates The notochord is an elongate, rod-like, skeletal structure dorsal to the gut tube and ventral to the nerve cord. The notochord should not be confused with the backbone or vertebral column of most adult vertebrates. The notochord appears early in the embryo and plays an important role in promoting or organizing the embryonic development of nearby structures. In most adult chordates the notochord disappears In some non-vertebrate chordates and fishes the notochord persists as a laterally flexible but incompressible skeletal rod that prevents telescopic collapse of the body during swimming.

Primitive Jawless Fish Lamphrey and Hag fish The most primitive of the chordates evident in the fossil record are the jawless Ostracoderms. They were jawless, bottom feeders Their endoskeleton was cartilaginous but the are covered with small bony plates They use a muscular pharynx to suck food into their mouths and to exchange gases in respiration. Their gill slits were permanently open

Jawless Fish cont. As the fish swam, this fin configuration drove the animal down into the bottom where its food was located. The bony plates were useful for protection but inhibiting when rapid swimming was required. They still had no axial skeleton These animals are long, slender eel like organisms. These animals exist either as bottom scavengers or parasites of other fish. (Hag fish top right)

Jawed cartilaginous fish The Chondrichthyes are the modern cartilaginous fish The present Chondrichthyes include the sharks, skates and rays. (Top left: skate Bottom left A ventral jaw with replaceable teeth. The limited mobility of the jaw means that the shark must thrash around to break up its prey Sharks must continually swim to avoid sinking. (Thought this was interesting!) The gills are not protected by an operculum

Cartilagenous Fish Cartilage is a soft, flexible material End of your nose, ears Cartilagenous fish have an entire skeleton made of it Class Chondrichthyes Sharks, skates and rays First jawed fish

Cartilagenous Fish Placoid Scales: tiny “teeth” that point towards posterior of animal Gill Slits: openings to the gills Skates, rays and some bottom-dwelling sharks have gill slits on ventral side Spiracles: openings that allow water to enter gill chamber Behind eye Mouth can be used to help spiracles pump water over gills

Cartilagenous Fish Fins More rigid than bony fish Pectoral fins in sharks provide lift In skates and rays pectoral fins are more developed

Skates and Rays Many species are bottom-dwellers Stingrays have a spine at the base of the tail that can inflict a stab wound Skates do not have spines Both eat crustaceans and mollusks

Sharks Group is more than 300 million years old Lateral line organ Used to detect motion in the water Ampullae of Lorenzini Sense electric fields generated by fish Teeth Constantly replaced Many sharks have to swim as they can not pump water over their gills

Sharks Reproduction Claspers Eggs Males use claspers to transfer sperm to females Located between the pelvic fin and body Eggs All sharks have eggs Some species have eggs that hatch internally and are then born live Some species lay an egg case known as a Mermaid’s Purse

Bony Fish Bony fish Skeleton made of bone Have vertebrae Have scales covered with mucus Barrier against infection and reduces friction with the water Found in every aquatic environment

Bony Fish Obtaining oxygen Use gills Located under a protective flap called the operculum Mouth and operculum open at the same time as water is drawn in by the mouth and passed over the gills

Bony Fish Locomotion Nekton Fins Peduncle As opposed to plankton Some are paired, others are single Paired: pectoral and pelvic movement Single: dorsal, anal and caudal Stabilization and thrust (power) Peduncle Used as a major marker for determining species Base of caudal fin

Bony Fish Pelagic v. Benthic Speed Pelagic refers to those living in the middle of the water column, open ocean Benthic refers to those living on the bottom Speed Depends on shape Faster fish have more sharp angles and bigger, forked caudal fins

Bony Fish Temperature Buoyancy Bony fish are ectothermic Their body temperature depends on the temperature of the environment Buoyancy Swim bladder Neutral buoyancy is when the fish neither sinks or floats Swim bladder contracts and fish sinks, bladder expands and fish rises

Bony Fish Feeding Digestion Parasitic (lamprey) Predatory Strainers (plankton-eaters Suckers (use change in volume to suck prey into mouth) Digestion One-way digestive system coupled with a closed circulatory system and 2-chambered heart

Bony Fish Reproduction Takes place during spawning Sperm and eggs are released into the water or fertilization takes place internally Eggs develop either floating or attached to a substrate