POLYDORA IN OYSTERS SUSPENDED IN THE WATER

Abstract

Among the numerous enemies of oysters the small Polychaete worms of the genus Polydora have long been considered as very destructive. It has been reported that sometimes these worms may be responsible for the complete disappearance of extensive oyster beds. Such depredations were described by (1890) and Roughley (1922, 1925) who were working in Australian waters, where Polydora caused a heavy mortality among the native oysters. Both authors identified the worm as P. ciliata. It is possible, however, that was mistaken in his identification of the species. According to Wilson (1928) Whitelegge found the ova and larvae of a species of Polydora attached alongside the adults to the walls of their burrows in oyster shells at Newcastle, in New South Wales. He believed the species to be Polydora ciliata Johns, but his figure of the egg-sacs resembles more closely that given by S6derstr6m for Polydora ligni If was actually mistaken then the destruction of the oysters in Australian waters should be attributed to at least two species of Polydora, namely, P. ciliata and P. ligni. Several species of Polydora are common along our Atlantic Coast. Lunz (1940, 1941) found that approximately 40 per cent of the oysters of South Carolina waters are infested with P. ciliata. This author states in his latest paper that he now has evidence or reports of infestation throughout the entire range of distribution of the American oyster, 0. virginica, in North America. Nelson and Stauber (1940) stated in a brief abstract that many oysters of New Jersey harbored P. ligni Webster. This appears to be the same species which, in the opinion of Wilson, was dealing with in Australia. Kavanagh (1940) found that the Japanese oyster, 0. gigas, planted in Louisiana waters became infested with P. ciliata. Takahashi (1937) reported that P. pacifica was quite commonly present in the shells of the pearl oyster, Pinctada margaritifera. Polydora or, as it is usually called, mud worm, is also known to infest shells of mollusks other than oysters. Lebour (1907) found that the mussels of the Northumberland beds of England were heavily infested with P. ciliata, and Field (1922) stated that the same species occurs in shells of the mussel, M. edulis, living in American waters.