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Sculptures by Phyllis Bone

FISH

CLASS CEPHALASPIDOMORPHI: Lampreys

The jawless lampreys have primitive chordate features such as a notochord, gill openings and metamerically segmented muscles. A cartilaginous cranium protects the brain and vertebrae protect the nerve cord. They have elongate bodies propelled by fins.

Lamprey

JAWED FISH

There are two classes of living fish with jaws: the Chondrichthyes (the cartilaginous fish or elasmobranchs) and the Osteichthyes (the bony fish). Both classes of fish have two pairs of lateral fins and a finned tail for propulsion in water. Their jaws and pharyngeal gill slits are large to obtain the oxygen and nutrients needed by their very active lives. The two classes of fish contain more living species than any other class of vertebrates! Members of two other early Classes the placoderms and acanthodians are now extinct.


CLASS CHONDRICHTHYES: Cartilaginous fish

Sharks, rays and chimaeras have a cartilaginous skeleton lacking bone. Placoid scales, formed from dermal denticles, cover their bodies. The external opening of the gill slits lacks a cover or 'operculum'. Their tails are usually heterocercal: the part of the fin below the vertebral column is larger than that above.

The cartilaginous skeleton of the ray (behind) shows the rostrum, the nasal capsules, the jaws and the branchial arches, which support the gills, and the spinal column.

The model of a shark (in front) shows the gill openings (without an operculum), the gills, their blood supply, the pumping heart and circulatory system.


Class Chondrichthyes

CLASS OSTEICHTHYES: Bony fish

The 'bony' fish have bony skeletons. Overlapping scales, lying under a thin layer of skin, cover the body. An operculum covers the external openings of the gill slits. Their tails are typically homocercal: the parts of fin above and below the vertebral column being equal. An internal swim bladder contains air and aids buoyancy.

Class Osteichtheyes

From left to right: a mounted trout, a trout skeleton and a cod skull show the typical features of the bony fish.


FISH BRAINS

Fish Brains

Top Left: Salmon brain (Class Osteichthyes)
Front Left: Dogfish brain (Class Chondrichthyes) -- Front Right: Lamprey brain (Class Cepalaspidomorphi)

The lamprey's simple brain has large olfactory lobes showing how a sense of smell must dominate its life. The brains of cartilaginous fish, like the dogfish, and bony fish, like the salmon, have large olfactory bulbs. Compared to lamprey brains, fish brains show a much greater development of the optic lobes and cerebellum, which are concerned with vision and balance respectively.