Water beetle : Any one of numerous species of aquatic beetles belonging to Dytiscus and allied genera of the family Dytiscidae, and to various genera of the family Hydrophilidae. These beetles swim with great agility, the fringed hind legs acting together like oars.

Example:


Taxonomy
water beetle, water beetles, free encyclopedia, aquatic, aquatic larvae, adults, larva, pupa, search, Unsourced, The rest, air bubble, abdomens, air supply, physical gill, gas exchange, Cybister, feelers.

Defination from the web:
Water beetle. From Wikipedia, the free encyclopedia. Jump to: navigation, search. This article does not cite any references or sources. ... b, head of beetle with feelers and gunts (Agabus); c, larva (Larva of Dyticus, Water Beetle); d, pupa (Pupa of Dyticus) ...