Reference: Biol. Bull., 138: 262-271. (June, 1970) MATURATION OF THE GONADS AND SEASONAL CYCLE OF THE PLANKTONIC LARVAE OF THE OPHIUROID AMPHIURA CHIAJEI FORBES x LUCIENNE FENAUX Chargee de recherche an C.N.RS. Station Zoologique, Villefranche-sur-Mer (06) Amphiura chiajei is a little Ophiuroid known in the Mediterranean Sea and in the Atlantic Ocean ; it is found from the coasts of Norway to Angola, also along the British Isles and Faroe and the Azores. It produces a planktonic larva, the development of which I have studied (Fenaux, 1963). Although this species is abundant in the Mediterranean, there are no previous records of the presence of its larvae. Only Miiller (1853) describes an ophiopluteus from the Adriatic Sea, which seems to be related to A. chiajei. In order to analyze the modalities of laying for a given species, it is as much important to know the conditions in which it takes place normally (and namely to precisely determine the periods during which the larvae appear in the plankton) as to follow the changes taking place during their gonad maturation. For this reason, in the course of my research on the ecological aspects of the reproduction of mediter-ranean Echinoids and Ophiuroids (Fenaux, 1968 b), I have studied the seasonal variations of gonads and the periodic presence of planktonic larvae of A. chiajei. These results appear in the present paper. MATERIALS AND METHODS For the study of maturation of their gonads, Ophiuroids were collected twice a month in samples of black mud from the inner basin of Villefranche Bay between April 1965 and March 1966. The seasonal cycle of their ophioplutei was ob-served in the plankton hauls made regularly over a period of three years (April 1961-April 1964) . The number of male and female ophiuroids whose gonads were examined be-tween April 1965 and April 1966 in either histological sections or smears is indicated below. A 65 M J A O N D J88 F M Males 12 34 28 17 27 26 15 18 29 28 9 Females 14 27 16 18 21 18 10 14 20 10 21 Indeterminable 33 1 The average size of the ophiuroids was 7 mm (diameter of the disc, arms not included) ; they were all dioecious. Gonads were examined either as smears or in 7 microns histological sections after fixation in the fluids of Bouin, Carnoy or 1 This study is derived from my state doctor's thesis on the ecological aspects of the repro-duction of Echinoids and Ophiuroids of Villefranche-sur-Mer, submitted in June 1968. 262
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