THE POLYCHAETE CERATONEREIS TRIDENT AT A AS A PEST OF THE SCALLOP AEQUIPECTEN GIBBUS HARRY W. WELLS AND MARY JANE WELLS Department of Biological Sciences, Florida State University, Tallahassee, Florida; and Department of Zoology, Duke University, Durham, North Carolina Because of the importance of clams, scallops, mussels, and oysters as a source of food, the biology of bivalve mollusks has received much attention. Much ecological research has centered on the associates of these bivalves, in recognition of the possibility that they may destroy the bivalves, or restrict their growth or reproduction, and, in this manner, may compete with man's fullest utilization of the bivalve populations. These potentially detrimental associates include predators that feed on the mollusk, fouling organisms that attach to the shell, commensals and ectoparasites that live between the shells, invaders that live in the shell itself, and endoparasites that live within the tissues and organs of the bivalve. The diverse organisms that can be termed "invaders" of the shell usually receive little consideration until, under optimal environmental conditions, a popula-tion "bloom" of the invader damages the shells sufficiently to cause mortalities or interfere with the processing or marketing of the shellfish. Outstanding examples of organisms that invade the shells of oysters are boring sponges (Cliona species), spionid polychaetes (Polydora species), and a fungus (Korringa, 1952). Usually the relation of such species to their host is quite distinct from that of the commensal or parasitic organisms, such as pinnotherid crabs, that live between the bivalve's shells. The species that invade the shell often have a detrimental effect upon their host, and to this extent, may consequently be considered parasites. Since 1958, the calico scallop has been the object of a small commercial fishery on the North Carolina coast ; however, the biology of this species has received little attention. Inasmuch as they can affect the population dynamics of the scallop, the enemies of this species, including its parasites, are important to this fishery. The spionid polychaete, Polydora ivebstcri Hartman, has long been considered a pest of bivalves. It penetrates the calcareous shells of oysters, scallops, and mussels, where its presence may stimulate the mollusk to secrete extra layers of shell around the worm's burrow. In this manner, Polydora causes its host to divert energy to shell deposition, detracting from its host's condition and suit-ability for market, and perhaps leaving its weakened host prey to other enemies and diseases (Lunz, 1940; Mackin and Cautheron, 1952; Medcof, 1946; Owen, 1957; and others). The typical deposits of shell around Polydora ivebsteri are termed "mud blisters" because of their characteristic dark color and mud in-clusions. In January, 1959, large brown 1 (listers were found in the upper valves of two calico scallops (Aequipccten gibbus), of a group of 20 which had been dredged off Ocracoke Island, North Carolina. The observed blisters contrasted with mud 149
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