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Reference: Biol. Bull., 160: 161-174. (February, 1981) PROTANDRIC HERMAPHRODITISM IN A MOLE CRAB, E MERIT A ASIATIC A (DECAPODA:ANOMURA) T. SUBRAMONIAM Department of Zoology. University of Madras. Madras-600 005, India ABSTRACT Protandric hermaphroditism in a mole crab, Emerita asiatica, is described. Neotenous males occur at 3.5 mm carapace length (CL) and above, whereas females acquire sexual maturity at 19 mm CL. The neotenous males, as they continue to grow, gradually lose male functions and reverse sex around 19 mm CL. The dis-appearance of genital papillae is the first visible sign of sex reversal; spermatogonial activity in testes ceases but hyperactivity of the mesodermic cells ensues. In the CL range of 19-22 mm, the male's gonad comprises inactive testicular and active ovarian portions; the median ovarian limb beyond the fused posterior extremity of the testes lacks testicular elements; and the vas deferens is intact but a pair of functional oviducts is formed. These intersexuals possess three pairs of pleopods. A few have eggs, and thus constitute secondary females in the population. Andro-genic glands, active in the neotenous males, show signs of degeneration in the larger males, and disappear in the intersexuals. The mesodermic cells of the gonad undergo important functional changes during sex reversal. Sex-changers with incomplete transformation of testis into ovary and imperfectly differentiated oviducts are also reported. INTRODUCTION In mammals the histogenesis of the gonad as an ovary or testis is determined by the sex genes that initiate chemical synthesis of substances responsible for sexual differentiation (Witschi, 1971). The malacostracan crustaceans are generally gon-ochoristic with genetically determined sex. But several of them exhibit both func-tional and non-functional hermaphroditism. Functional protandric hermaphrodit-ism has been well documented in the deep-sea prawns and two isopod groups, Cymathoides and Cryptoniscidae (Yaldwyn, 1966; Charniaux-Cotton, 1975a). Here, each sex possesses complete genetic information for the morphogenesis of both sexes. The genes for male morphogenesis act in the presence of an androgenic gland hormone and for females in its absence (Charniaux-Cotton, 1960a). Other groups of crustaceans may well show change of sex with growth, but evidence is rather meager. Mole crabs, including various species of Emerita, are typical burrowing forms on the wave-washed sandy beaches of temperate and trop-ical seas. Several species show sexual dimorphism in size. For example, the males of E. asiatica acquire sexual maturity soon after their metamorphosis from meg-alopa larvae (3.5 mm carapace length, CL) while the females attain it after con-siderable growth (19-22 mm CL) (Subramoniam, 1977). This size distinction at sexual maturity of Emerita is considered a characteristic feature of the genus by Efford (1967). Barnes and Wenner (1968), on the contrary, proposed a protandric hermaphroditism based on sex-ratio studies on E. analoga. However, the sex ratio Received 14 January 1980, accepted 3 October 1980. Abbreviations: CL, carapace length. 161




T Subramoniam
Biol Bull 160: 161-174 (1981)

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