Distribution:
Found in both marine and freshwater, including the cool waters of the Northern Hemisphere, and disjunctly in deep waters of the southern hemisphere off New Guinea, New Zealand and eastern Australia.
Habitat:
Benthic, in a variety of habitats, from fresh waters and the intertidal to bathyal depths, found over a variety of bottom types.
Anatomy
Kidneys lack glomeruli.
Remarks:
This is a diverse family with more than 70 genera and 300 species. Most species are small, but the giant in the family attains about a meter in length. Many species have internal fertilization, although all are oviparous.