Spermatophore Transfer in the Dioecious Tidal Snail Cerithidea rhizophorarum (Gastropoda: Potamididae)

摘要

Cerithidea rhizophorarum A. Adams, 1855 belonging to the family Potamididae, is a dioecious tidal snail, occurring throughout the western coasts of the tropical Pacific Ocean to the northernmost part of Honshu Island, Japan. Snail mating can be categorized as face-to-face mating or shell-mounting mating (Asami et al, 1998). C. rhizophorarum mates by shell mounting (Wakamatsu & Tomiyama, 2000). Ohtaki et al. (2001) and Takeuchi et al. (2007) observed that C. rhizophorarum shows random mating by shellsize. When C. rhizophorarum copulates, a male mounts the shell of a female and inserts its soft body into that of the female (Wakamatsu & Tomiyama, 2000). Even by dissection of fixed specimens, however, we did not find copulatory organs such as the penisor vagina clearly in males or females. It remained unknown how the male transfers sperm to the female without copulatory organs. In the Mollusca, sperm transfer can be categorized as direct injection of sperm liquid or spermatophore translocation (Tompa, 1984). It had not been determined whether C. rhizophorarum forms a spermatophore. During the field observations on copulatory behavior of this species, we confirmed spermatophore transfer between male-female pairs. In this paper, we report the morphology of spermatophore and the manner of spermatophore transfer in C. rhizophorarum.