1. Chordates and Vertebrates

2. 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.

3. 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

4. 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)

5. 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

6. 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

7. 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

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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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