On the occurrence of protandric hermaphroditism in the mollusc Crepidula fornicata

Abstract

Crepidula fornicata is a streptoneurous Gastropod belonging to the Calyptræidæ, a family of the Tænioglossa. It was first introduced into England from America about 1880 (1), when it was imported with American oysters. In America it is found on the east coast from Labrador to Florida, but in England so far as is known, it is confined to the Essex and Lincolnshire coasts, occurring, however, in abundance in shallow water in the neighbourhood of the mouths of the Crouch and Blackwater rivers. The conditions on the Essex coast seem to be highly favourable for its growth and propagation; indeed, so favourable, that within five or six years it has over-run the oyster beds at West Mersea. By attaching themselves very strongly to oyster-shells they cause the oyster fisherman much trouble, and it may be remarked, by competing for food and oxygen with the oysters may become a cause of much more serious trouble in the future. To obtain food the animals raise the anterior part of their shell and extending the head to the front edge of the shell, move it slowly from side to side: at times the whole shell may be similarly turned slowly round to the one side or the other. Crepidula fornicata is sedentary for the greater part of its life. It forms "chains," as Prof. Conklin calls them, by the curious habit the individuals have of fixing themselves in linear series one on the top of another as in fig. 1. Chains of as many as 12 individuals have been found. Viewed as a whole, a chain is seen to form a spiral of about half a trun, bending over to the right.