31.1    Vertebrates

	There are about 43,000 living species.
	All vertebrates have endoskeletons.
	An endoskeleton grows as the animal grows.
	The earliest known vertebrate fossils are animal called ostracoderms.

31.2    The Natural History of Fishes

	Mineral deposits make bone heavy and rigid.
	Since they first evolved, cartilaginous fishes have changed little whereas bony fishes have changed a great deal.
	The difference is the variations in their environment.

31.3    Jawless and Cartilaginous Fishes

	Chrondrichthyes means "cartilage fishes."
	This includes sharks, rays and skates, all of which have skeletons made almost entirely of cartilage.
	The spiral valve slows the movement of food through the short intestine.
	Sharks must swim constantly to avoid suffocating.
	In sharks and other vertebrates, excretory structures are combined in a pair of organs called kidneys.
	The lateral line system detects changes in pressure and vibrations in the water.
	This system also provides sharks with information about the movement of other animals and objects in the water.

31.4    Bony Fishes

	Coelacanth remains the only known living species of lobe-finned fish.
	Australian lungfish comes to the surface to gulp air when the water has too little oxygen.
	The lungfish forms cocoons out of mud and mucus when streams dry up.
	Ray-finned fishes are considered to be the most sucessful group because they have adapted to every kind of aquatic environment.
	They have radiated into thousands of species.
	All of their scales point toward the posterior.
	This helps reduce friction as the fish swims forward.
	A layer of mucus covers the scales to aid in insulation and provide a protective, waterproof covering for the body.
	Swim bladder and movable fins enable fish to remain in the same spot.
	Fishes body temperature is mainly regulated by their external environment.
	Only the fastest, strongest and best-adapted young survive to produce offspring and continue the species.

31.5    The Life Cycle of a Salmon

	Fishes of the salmon family are long-distance travelers to include trout, char and smelt.
	Salmon hatch in fresh water, spend adult life at sea and return to fresh water to spawn.

Back to course outline