KINGDOM ANIMALIA Phylum Chordata Subphylum Vertebrata Superclass Osteichthyes

Vertebrate Classes

Class Actinopterygii Ray-finned fishes Most bony fishes and largest single group of chordates (24,000 species) Well-adapted; successful in marine and freshwater Carnivores, herbivores, parasites, and scavengers

Features Well-developed lateral fins Fins contain delicate bony rays extending from internal skeleton Provide support and articulation Caudal fin provides thrust and other fins stabilize

Features Scales = light bone (small or absent in fast swimmers) Swim bladder (lung) saclike extension of digestive tract during development used to retain gases to provide fish with buoyancy (don’t sink, energy saving) may also be used for atmospheric respiration Gills to maximize area for gas exchange Covered by bony operculum Force water over gills when not moving

Features Acrodin-covered teeth Circulation Brain 2-chambered heart Blood flow under low pressure Blood flows in opposite direction as water in gills, which maximizes oxygen saturation Brain Sensory and to some extent motor coordinating centers well developed Overall coordinating and reasoning centers are primitive

Examples Primitive: heavy scales, use swim bladder for respiration in stagnant waters Bichir - freshwater Africa Gar - Kansas Paddlefish - N. Am. Sturgeon - N. Am. Bowfin - N. Am.

Examples Derived: Dominant fishes today; extremely diverse (morphology); upper jaw protrusible, thin/flexible scales, swim bladder for buoyancy Herring (predator) Coral reef fish (lateral compression) Flounder (very laterally compressed, swim on side, eyes on upper body) Moray eel (tubular, sacrifice speed for agility)

Class Actinistia Only one marine species remains in this ancient lineage Lobe-finned fish called a coelacanth Only living chordate with a movable intracranial joint divides skull into anterior and posterior halves may allow upper jaw to elevate Fatty swim bladder (some buoyancy) Predator Enamel-covered teeth

Coelacanth Thought to have been extinct until discovery in Indian Ocean in 1938 Since then, recovered 70+ Live in underwater lava caves at depths of 200-300 meters Compared to fossil evidence, not many changes-habitat stable (molecular level unknown)

Class Dipnoi Lobe-finned fishes Reduced skeleton Teeth modified into plates (enamel) Intracranial joint is immobile Swim bladder highly vascularized and used as a lung

Lungfishes 6 species of freshwater lungfishes found in tropical regions of Africa, Australia, and S. America Areas subject to drought Some use lungs when conditions unfavorable, use gills otherwise In others, gills reduced and dependent on lungs

African Lungfish Burrows in mud when water dries up Secretes a mucous cocoon around its body with air hole at tip Can survive up to 4 years

Tetrapod Ancestors Response to periodic drying or to avoid predation/competition in aquatic habitat Limbs further developed as stayed on land Few competitors, no predators—selective pressure in favor of the land move 2 features: Functional lungs (as well as gills) Fleshy lateral fins containing muscle to support body and provide mobility

Tetrapod Ancestors Skeletal bones in fins similar to bones of primitive tetrapods Limbs thought to have developed in the water, not on land