Mysidopsis jenseni n. sp. from the Pacific coast of Washington, with first description of female M. intii Holmquist, 1957 (Crustacea: Mysida: Mysidae).

Mysidopsis jenseni n. sp. is described from the Puget Sound area, Washington, USA from sand/rocky bottoms in depths of 8 to 15 m. This new species increases the number of American Pacific species of Mysidopsis to eight. Based on a collection of M. intii Holmquist, 1957 from coastal waters of Chile, a supplementary description of the male is presented and the female is described for the first time. The presence of a mid-dorsal lappet near the posterior margin of the carapace of females only distinguishes the new species from all other Mysidopsis species except M. velifera Brattegard, 1973 from the Caribbean. M. jenseni is further separated from its American Pacific congeners by the following combination of characters: antennal scale 34 times as long as wide with a rounded apex and distal suture; uropodal endopod with 89 spiniform setae along ventromedial margin; telson with 4654 spiniform setae along all margins. The presence of lobe-like protuberances on the basis and dactylus of thoracic endopods 38 was documented for the new species, M. intii and other species of Mysidopsis as well as species belonging to the other four genera within the Tribe Mysidopsini. A key to the species of Mysidopsis of the Pacific coasts of the Americas is given.