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| Fishes |
| There are about 25,000 described species of fishes living today, more than the number of species in all other vertebrate groups combined. Ichthyologists (biologists who study fish)have various definitions for what a fish is, but the most basic would be as "aquatic vertebrates that have gills throughout life and limbs, if any, in the shape of fine" (Nelson, 1994). Some ichthyologists exclude the agnatha (jawless vertebrates such as lampreys and hagfish ) from the fishes, but we include them here as one of five classes of extant (living) fishes. |
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| Epinephalus tauvina, class Osteichthyes |
See also: Fish body structures Measuring fish Fish tails and fins Fish head structures Fish body and mouth types Fish teeth and gill structure |
 | Carcharodon carcharias, great white shark, class Chondrichthyes |
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Fishes as a group are extremely diverse in form, physiology, behaviour
, trophic
position, habitats,
and general life history. Fishes of the Osteichthyes
(bony fishes) include an enormous
variety of shapes and sizes, however, a generalized form that comes to mind for most people
might be one similar to
Epinephalus
tauvina
(a member of the sea bass
family, the Serranidae
). The class Osteichthyes
contains most of the
species of extant (living) fishes.
The sharks , rays , chimaeras , and their relatives are members of the class Chondrichthyes , the cartilaginous fishes, and consists of about 800 species worldwide. There are several other groups of living fishes, including the sarcopterygii (lobe finned fishes, such as lungfish and Coelacanths ), the myxini (hagfish ), and Cephalaspidomorphi (lampreys ). References: Moyle & Cech, 1982 Nelson, 1994 |
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