The reproductive biology of deep-sea forcipulate seastars (Asteroidea: Echinodermata) from the N.E. Atlantic Ocean

Abstract

Samples of the deep-sea forcipulate seastarsBrisinga endecacnemos, Brisingella coronata, Freyella spinosaandZoroaster fulgenshave been collected at a number of stations in the N.E. Atlantic. Examination of their reproductive biology suggests subtle interspecific variations in their gametogenic cycles. The gonads ofBrisinga endecacnemosare serially arranged under the dorsal arm surface, each cluster of gonad tubules having its own gonopore. In the closely relatedBrisingella coronataeach gonad consists of up to 12 elongate tubules opening at a single gonopore at the dorsal surface. In both species the maximum egg diameter is about 1250 μm and fecundity may be up to 60000 eggs per individual. It appears that the eggs inBrisinga endecacnemosare produced in clusters whilst those ofBrisingella coronataare produced continuously. InFreyella spinosathe gonad consists of a small tubular sac analogous to a single tubule ofBrisinga endecacnemos.Maximum fecundity is only 2500 eggs per individual, and the maximum egg size is 1250 μm. In all three species eggs that are not spawned undergo internal oocyte degeneration. The gonads ofZoroaster fulgensshow the typical asteroid configuration of two at the base of each arm, one either side of the ambulacrum. The maximum oocyte diameter is 950 μm. There is some evidence that there may be a seasonality of reproduction in this species. In all four species examined the large egg size and relatively low fecundity suggest direct demersal development with the subtle variations in their reproductive biology reflecting slightly different breeding habits.