Stylochus tripartitus Hyman 1953

Stylochus tripartitus Hyman, 1953 Stylochus tripartitus Hyman, 1953a: 281–284, figs 10–12 (type locality: Pacific Grove, California). Distribution From Coos Bay, Oregon, to El Mogote, Baja California Sur. Habitat Epibiont and benthic (kelp rhizoids and under shore rocks). Remarks Stylochus tripartitus is characterized by a light brown coloration covered with brown streaks, marginal eyes distributed in the first third of the anterior region of the body, tentacular and cerebral eyes, and nuchal tentacles. The male reproductive system features a tripartite seminal vesicle and a small penial papilla. The female reproductive system lacks a Lang’s vesicle. Stylochus tripartitus is one of the two Californian species of the genus Stylochus with a tripartite seminal vesicle. The other species is S. exiguus Hyman, 1953, which is very small and has marginal eyes that surround the body margin. Stylochus tripartitus differs from S. mistus primarily in color and coloration pattern.