COPULATION BY HYPODERMIC INJECTION IN THE NUDIBRANCHS PALIO ZOSTERAE AND P. DUBIA (GASTROPODA, OPISTHOBRANCHIA).

The Pacific nudibranch Palio (= Polycera) zosterae and the Atlantic P. dubia copulate in a manner different from that of most nudibranchs. Nudibranchs are hermaphroditic and normally copulate reciprocally, with the intromittant organ of one inserted in the vaginal opening of the other. P. zosterae and P. dubia lack a complete vaginal duct. Copulation is usually reciprocal but involves the piercing of the body wall by a barbed, eversible penial cirrus. If the cirrus injects exogenous sperm into the body wall or the haemocoel, the sperm are phagocytosed by blood cells. If the cirrus penetrates the gonad, exogenous sperm may be injected into a spermatogenic acinus. After traveling down the hermaphroditic duct to the anterior reproductive organs, these sperm presumably are sorted from endogenous sperm and stored in the receptaculum seminis. The organization of the reproductive system in Palio differs markedly from that in members of the closely related genus Polycera.