This report is part of a sub-series to aid biology students, biologists, biological oceanographers, and informed laymen in the identification and study of marine flora and fauna of the Northeastern United States. Contents of this report include: (1) Introduction; (2) Glossary; (3) Key to the marine lernaeopodoid copepods of the Northeastern United States; (4) Annotated systematic list; (5) Selected bibliography; (6) Systematic index; (7) Acknowledgments; and (8) Coordinating Editor's comments. The "Order Lernaeopodidea" consists of four families of parasitic copepods. The lernaeopodoid Copepoda consists of some 300 species of extremely transformed copepods that are all parasites of fish known to fishermen as "gill maggots." Many species are vaguely known. This report presents a key to the sixteen species of lernaeopodoid Copepods that have been reported on fishes from Maine to Virginia. The key is only for the females because the dwarf male is characteristically attached to its female partner. The annotated systematic lists give known hosts for each of these 16 species. (MR)