Bio Review Notes

Bio Review Notes #89
FISHES

Fishes are aquatic vertebrates that have fins and gills throughout their adult lives. They are a very heterogeneous assemblage of 4 distinct classes:
the jawless fishes (Agnatha); the extinct, armored Placodermi; the shark-like or cartilaginous fishes (Chondrichthyes); and the bony fishes (Osteichthyes).

General characteristics of fishes:

Central nervous system protected by enclosure inside skeleton.
Free-swimming by means of side-to-side undulations of the body.
Gills used in respiration; but most fishes no longer filter feed.

Class Agnatha: Jawless fishes, often with a filter-feeding larval stage. Extinct forms were often heavily armored and continued to filter-feed as adults. Modern forms (cyclostomes) include lampreys and hagfishes, both eel-shaped and parasitic on other fishes: lampreys suck blood; hagfishes eat their way through the flesh of their victims.

Class Placodermi: An extinct group in which jaws first evolved. Paired fins also evolved in this group and are retained in all further vertebrate classes. Many placoderms were predators from 6 inches up to 50 feet long.

Class Chondrichthyes: Cartilaginous fishes, including sharks, skates, and rays. Bone is reduced to a series of tooth-like denticles embedded in the skin. The rest of the skeleton is made of cartilage only.

Class Osteichthyes: Bony fishes, including the vast majority of fishes. Scales and internal skeleton are both usually bony. A wide variety of sizes, shapes, and habits occurs in this group.

Index Syllabus

rev. July 2010