Aspects of sexual biology of the anomuran crab emerita asiatica

Male Emerita asiatica Milne Edwards are smaller than females. The secondary sexual characters of males and females are described in detail. Applying the method of Wenner (1972), sex ratio is calculated. The overlap in size range between males and females is too wide to suggest sex reversal. An analysis of secondary sexual characters in post-larval juveniles during megalopa settlement corroborates the view that males and females develop separately from the megalopa. The males acquire their sexual maturity soon after metamorphosis from the megalopa stage, whereas the females attain their sexual maturity only after considerable body growth. the males continue to grow to attain a maximum carapace length of 11 mm; they do not show any tendency towards changing their sex. This is evidenced by the fact that the weight increase of the gonadal apparatus is directly related to the increase in the male carapace length (CL) and body weight. On the other hand, retention of larval characters such as short eye stalk, toothless chelae of the fifth leg (in males up to 5 mm CL), together with the very small size suggest that the males are neotenic. Only males up to 5 mm CL were found to take part in mating. During mating, as many as 5 tiny males deposit their spermatophores in the pleopodal region of one female. This type of mating assures effective transfer of spermatophores in the turbulent environment inhabited. Spermatophores are pedunculate and embedded in a gelatinous matrix to form a long ribbon. There are two types of spermatophores in the ribbon, and they differ in detail from those of other anomuran species. The spermatozoa are rod-like, with a club-shaped acrosomal head. Five spines originate from the junction between head and body. The mode of sperm release from the spermatophores is described; oviducal secretion may be responsible for opening the spermatophore.