The pirate perch is the only species in this family. It is a small fish typical of slow-water, weedy habitats. It is characterized by a single dorsal fin with both spines and rays, rough scales over its entire body, and its most distinctive feature, its anus below its opercula. In New York it is found in two areas: tributaries to the Great Lakes and on Long Island. Individuals are sufficiently different in appearance to be treated as subspecies and both subspecies are native to the state. The western form is rare.
Pirate Perch resides in low-gradient streams with clay or sand and some heavy debris. The western subspecies (gibbosus) is native in two of 18 watersheds in western and central NY. It has declined to levels below detection in the Erie watershed but has increased in tributaries in the Ontario watershed. It is classified as Species of Greatest Conservation Need. The eastern subspecies (sayanus) lives in streams and ponds of Long Island but is no longer found in the westernmost streams.