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  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  As opposed to plankton  Fins  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  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  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  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