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Fishes - The class includes the sharks skates and rays Gas...

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Fishes Fishes are aquatic animals with a streamlined shape and a functional tail that allow  them to move rapidly through water. Fishes exchange gases with their environment  through  gills , although a few species have lungs that supplement the gills for gas  exchange.  One class of fishes called  Agnatha  is made up of species that have no jaws. Lampreys  and hagfishes are species within this class. These fishes feed by sucking blood and  other body fluids from their prey, usually other fishes.  Another class of fishes is  Placodermi . The placoderms are now extinct and are  recognized as the earliest known fishes with jaws. Placoderms were freshwater bottom- dwellers with a partially bony endoskeleton and bony, armored plates. Another class of  fish is  Chondrichthyes . These fishes have endoskeletons composed entirely of cartilage. 
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Unformatted text preview: The class includes the sharks, skates, and rays. Gas exchanges are made at several prominent, vertical gill openings on either side of the throat. The bony fishes belong to the class Osteichthyes . Most of the familiar fishes living today are bony fishes. They live in the oceans (for example, tuna, mackerel, and herring) and in fresh water (for example, striped bass, trout, and goldfish). The bony fishes prospered during the Devonian Period, which is also called the Age of Fishes. Bony fishes have gills as well as fleshy pectoral and pelvic fins. The ray-finned fishes are the predominant type of bony fishes living today. These fishes have a swim bladder , which is a gas-filled sac near the gut that permits a fish to change its buoyancy....
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