Phylum Chordata

Subphylum Vertebrata

Infraphylum Gnathostomata

• Class Placodermi (Paleozoic armoured fishes)– Extinct

• Class Chondrichthyes (Cartilaginous fishes)– Sharks & rays

• Class Ostichthyes (Bony fishes)– Subclass Actinopterygii (ray-finned fishes)– Subclass Sarcopterygii (lobe-finned fishes)

Features of the “Fishes”

• Complete gut• Respiratory

System• Closed

Circulatory System– 2 chambered

heart• Electroreception

– Passive– Active

Class Placodermi (Paleozoic armoured fishes)

• Ex: Dunkleosteus terrelli

• 33ft long, 4 tons

• Extinct. Lived in the Paleozoic era

• Thought to be the largest predatory fish.

Class ChondrichthyesThe present Chondrichthyes include the sharks, skates and rays. • Features of this group include:

– Skeleton made of cartilage– A ventral jaw with replaceable teeth. The limited mobility of the

jaw means that the shark must thrash around to break up its prey. – A heterocercal tail drives the animal upwards as it swims. – Does not have swim bladder for buoyancy (although the large

lipid filled liver provides some resistance to sinking). This means the sharks must continually swim to avoid sinking.

– The lateral fins are well developed to control pitch but are not for braking. In the skates and rays, the lateral pectoral fins have been greatly enlarged and the animals beat them like wings when swimming.

– Well developed sensory system that permits rapid and accurate detection of danger or prey at a considerable distance.

Class Chondrichthyes (Cartilaginous fishes)

All globally vulnerable to extinction

A third of oceanic shark species are now at risk of extinction, according to the World Conservation Union (IUCN). Their fins are highly prized in Asia for making shark-fin

soup

• Class Osteichthyes (Bony fishes)– Subclass Actinopterygii (Ray-finned fishes)– Subclass Sarcopterygii (Lobe-finned fishes)

Subclass Actinopterygii (Ray-finned fishes)

• The largest single group of chordates, with over 20,000 living species. – carnivores, herbivores,

parasites and scavengers.

• The caudal fin provides a powerful lateral of forward thrust. The pectoral and pelvic fins act as stabilizers.

• The swim bladder provides the fish with a neutral buoyancy. • Extensive gills to maximize the surface area for gas exchange.

– Use a counter current system where the blood in the gill capillaries flows in the opposite direction to the water flowing over the gills . This allows for a higher saturation of the blood with oxygen.

• A bony operculum provides protection for the delicate gill tissues and by moving the operculum, water can be forced over the gills without the fish being compelled to move.

• A two chambered heart means that the blood flow to the body is under very low pressure.

Example: Angler Fish

• Live deep in the ocean or on continental shelf

• Only females found…why?

Subclass Sarcopterygii (Lobe-finned fishes)

• Precursors to four limbed organisms (tetrapods).– Pectoral and pelvic fins

have articulations that resemble those of tetrapod limbs.

• Many early sarcopterygians have a symmetrical tail.

• All sarcopterygians possess teeth covered with true enamel.

Coelacanth

Example: Lungfish

• Has a set of gills and one lung!

• Able to survive and breath air for at least two days

• Allows the lungfish to survive in times of drought or other severe conditions.

African lungfish