Variation and abnormality of genital system in Littorina sitkana Philippi (Mollusca, Gastropoda) in Northern Japan

The anatomy of Littorina sitkana was examined using specimens from nine loc alities in northern Japan. These localities are known to be genetically clu stered into two geographic groups; the first group consists of localities o n the northern coast of Hokkaido along the Seas of Japan and Okhotsk and th e second one comprises localities on the Pacific coasts of Hokkaido and Hon shu. Anatomical surveys revealed that the mean numbers of penial glands dif fer significantly between the northern and Pacific sites, in correlation wi th the genetic variation. On the other hand, the mean relative size of the capsule gland within the pallial oviduct was positively correlated with mea n sea-surface temperature, almost independently of the genetic difference. In addition, imposer was found for the first time in C. sitkana. Females fr equently lacked the capsule gland in the imposer-present populations. The m ean relative size of capsule gland to the whole pallial oviduct was signifi cantly smaller there than in the imposer-free populations. The number of pe nial glands in males tended to be small in the imposer-present populations. The penis of imposer females was much shorter than that of males, in contr ast to Nucella species occurring sympatrically on these coasts, in which th e female penis is nearly as long as the male one. Although the pallial ovid uct is reported to be replaced by a prostate gland in imposer females of Li ttorina littorea, such replacement was not found in any imposer female of L . sitkana.