Relative growth and sexual maturity of Ilia nncleus (L.) (Crustacea, Decapoda) By Mario Mori Mori, M. (1994): Relative growth and sexual maturity of Ilia nncleus (L.) (Crustacea, Decapoda). -Spixiana 17/1: 21-26 Morphological Variation related to sexual maturity is examined in the little crab Ilia nucleus (L.), captured in the Northern Tyrrhenian Sea (Central Mediterranean) at 8 m depth in a sand biocoenosis characterized by prairies of Cymodocea nodosa (Ucria). Five morphometric relationships were investigated on 25 females and 19 males, ranging from 10 to 23,5 mm and from 10 to 25 mm carapace width (CW), respectively. Sexual dimorphism was demonstrated for all examined morphometric characters. The carapace and the abdomen are respectively longer and larger in females than in males. The chelae are longer in males than in females. The male body is higher than the female body in juvenile individuals, while in the adults the body becomes higher in females than in males. In the juvenile individuals the chelae are longer in females than in males, while in the adult specimens they appear longer in males than in females. The female abdomen grows remarkably at the puberty, forming an abdominal Chamber. Pubertal moult females were observed in the size ränge of 12.7 -13.9 mm CW, while the male one was estimated to occur at about 15 mm CW. The possibility that the pubertal moult in Ilia nucleus is terminal or not is discussed. Mario Mori, Istituto di Anatomia Comparata dell'Universitä, Viale Benedetto XV 5, 16132 Genova, Italy Introduction Relative growth has been investigated particularly in crustacean brachyurans species (Hartnoll 1974, 1982, Cau et al. 1981, Abelö & Sardä 1982), and in a variety of ways (see Gore & Scotto 1983), but it has been mainly studied in order to estimate the onset of sexual maturity (Watson 1970, Hartnoll 1972, 1982, Arnaud & Do Chi 1977, Mori 1986 a, b, Gaertner & Laloe 1986, Vannini & Gherardi 1988, Felder & Lowett 1989, Abellö et al. 1990). The only informations available on the biology of Ilia nucleus (L., 1758) (Brachyura, Leucosidae) are records of ovigerous females (Zariquiey Alavarez 1968). In this paper we investigated the relative growth of the crab I. nucleus captured in the Northern Tyrrhenian (Central Mediterranean) with the principal aim to estimate the size ränge over which the pubertal moult may occur and whether this moult is terminal or not. Materials and Methods The crab (25 females and 19 males) were caught by mean of an otter trawl, during an one hour haul, on March 1986, at 8 m depth, in a sand biocoenosis characterized by prairies otCymodocea nodosa (Ucria), in front of the Ombrone river (North Tyrrhenian Sea, Central Mediterranean). The size of individuals collected ranged from 10 to 23.5 mm carapace length for females and from 10 to 25 mm CL for males. 21
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