The parasitic copepod Ismaila monstrosa Bergh is recorded from the ascoglossan opisthobranch Ercolania funerea (Costa). One specimen of E.funerea from St. Thomas, U. S. Virgin Islands, contained one egg-bearing female and one male copepod. This is the first record from the type locality since the original description of I. monstrosa, and the first certain record of an identifiable endoparasitic copepod from an ascoglossan. All records of endoparasitic copepods from shell-less opisthobranchs are listed. Some systematic problems of the family Splanchnotrophidae are discussed. Keys to generic identification of females and males of the four genera of copepods occurring as endoparasites of shell-less opisthobranchs are presented.