Chordates and Vertebrates

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
• 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 Mermaids
  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
• 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

15
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

16
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

17
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

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