REPRODUCTION IN TWO SYMPATRIC SPECIES OFMACOMA(BIVALVIA)

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Abstract
Comparative reproduction in 2 infaunal intertidal clams of the family Tellinidae, M. secta and M. nasuta was studied on a sand flat in northern California [USA]. Fortnightly samples were taken for 13 mo. and gonads were prepared for histological examination. Seasonal gonadal changes were reported, as well as the physical and biotic factors which may have influenced them. The 6 stages of gonadal development for Macoma were described and the seasonal timing of these stages was compared between the 2 spp. M. secta spawned in mid Aug. and M. nasuta spawned in May and from Sept. through Nov. Spawning probably took 2-3 wk for M. secta individuals and 1 or 2 days for M. nasuta individuals. One to one sex ratios were found for each species. M. nasuta females are characterized by noncellular spherical inclusions in follicle cells which are probably nutritive in function. The changing time of spawning on a latitudinal gradient for M. nasuta follows a previously published predictive model.