Fishes
Superclass PISCES
(Gnathostomata, in part)
Jaws derived from modified gill arches; gills present throughout life, covered
with ectoderm and directed externally; gill arches not fused with neurocranium;
median and paired fins usually present (secondarily lost in some groups); ears
with 3 semicircular canals; vertebral centra usually present; eyes usually well
developed (secondarily reduced or absent in a few groups).
The fishes represent one of the two divisions of the Gnathostomata; the
other division comprises the tetrapods (amphibians, reptiles, birds and mammals). Two classes of fishes are recognised: the Chondrichthyes (sharks, rays
and chimaeras) and the Osteichthyes (bony fishes).
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