Stylochus (Stylochus) atentaculatus Hyman 1953

Stylochus (Stylochus) atentaculatus Hyman, 1953 Stylochus atentaculatus Hyman, 1953a: 283–286, figs 14–17 (type locality: San Mateo Beach, California, United States). Stylochus atentaculatus – Brusca 2005: 70 (new record from San Lorenzo Channel, La Paz Bay, Baja California Sur, Mexico, checklist). Distribution San Mateo, Charleston, Cape Arago State Park, Oregon; San Nicolas Island, California, United States; San Lorenzo Channel, La Paz Bay, Baja California Sur, Mexico. Habitat Benthic (collected in rocky hollows in San Mateo, California, at a depth of 51.2064 m on San Nicolas Island, California; between 5.48 and 9.11 m in the San Lorenzo Channel, Gulf of California; in the intertidal zone in Oregon). Remarks Stylochus (Stylochus) atentaculatus is characterized by an elongate oval body with a dark brown coloration with dots, marginal eyes distributed throughout the periphery of the body, cerebral eyes arranged in two lines and tentacular eyes distributed in a circular manner, and round nuchal tentacles. Hyman (1953a) described that the nuchal tentacles is only present in juveniles and in adult organisms this character is not observed; Hyman considered that in adult specimens the tentacles are fused with the dorsal surface. The male reproductive system features a simple (not tripartite) an elongated seminal vesicle, a prominent oval prostatic vesicle; wide male atrium. The female reproductive system has a tubular female atrium, an elongated and prominent vagina, with the central region of the vagina characterized by a highly scalloped muscular wall.