GONAD MATURATION AND SEXUALITY IN THE WEST AFRICAN BLOODY COCKLE, ANADARA SENILIS (L.)

Gonad maturation and sexuality in Ghanaian populations of Anadarasenilis were studied by means of macroscopic examination ofthe visceral mass, microscopic examination of smears of sexualproducts and by histological methods. Sexual differentiationinto either distinct male or female, begins at a shell lengthof 10–12mm. Only 1% or less have both ovary and testis.First spawnings take place at shell size 18–20mm. Althoughin tidal lagoons the sex ratio is 1:1, in the adverse conditionsof closed lagoons, the male to female ratio is about 1:2. Unbalancedsex ratios recorded in a population in Lagos, Nigeria, led aprevious worker to the conclusion that the species is a protandrichermaphrodite.It is argued here that hermaphroditism is an insignificant featurein A. senilis and that the species is basically gonochoristic(dioecious). ^* PRESENT ADDRESS: Department of Zoology, University Collegeof Swansea, Swansea SA2 8PP, Wales (Received 16 June 1981;     

REPRODUCTIVE CYCLES OF CERASTODERMA GLAUCUM(BRUGUIERE) AND C. EDULE (L.) WITH SPECIAL REFERENCE TO THE EFFECTS OF THE 1981-82 SEVERE WINTER

Gonadal changes in two species of Cerastoderma occurring indiscrete populations in South Wales were monitored by stereologicalanalysis during the breeding seasons of 1981 and 1982. Fecundityand spawning efficiencies were determined quantitatively. Therelationship between reproductive activity and changes in meatcondition are discussed. Both species are opportunistic breeders. Their normal patternsof reproduction are similar, consisting of minimum activityin winter and peak activity during spring/early summer. Thetwo species were affected differently by the severe winter of1981–82—C. glau-cum exhibited a single, ‘epidemic’spawning and resumed gametogenesis after a 4-month resting period.C. edule adopted a ‘polycyclic’ pattern withouta resting period. Both of these unusual reproductive strategies,augmented by reduced predation resulted in heavy spatfalls. (Received 20 March 1985; revised 20 March 1985;