Botryllophilus bamfieldensis, new species, is described on the basis of specimens of both sexes living in a compound ascidian from the Bamfield area in Barkley Sound, west coast of Vancouver Island, Canada. The morphological details of the female fit the diagnostic features for morphotype A of the genus. The female can be distinguished from its eight congeners by the sharply pointed triangular apex of the cephalosome, the weakly segmented metasome, and the markedly elongated exopods of left legs 1–4. The male of the new species differs from the only known male of a species of morphotype A (B. abbotti) in that the endopod of leg 1 bears five variously shaped spines and five plumose setae. It is proposed that females of nine species of morphotype A be further divided into two subgroups based on two patterns of armature for legs 1–4.