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 thesharks, 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.
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 oncontinental 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 onelung!• Able to survive and breathair for at least two days• Allows the lungfish tosurvive in times of drought orother severe conditions. African lungfish