The Nemertean Carcinonemertes as an Indicator of the Spawning History of the Host, Callinectes sapidus

Abstract

In the course of biological studies of Callinectes sapidus Rathbun, the blue crab or common commercial crab of Chesapeake Bay, notes were made on the parasitic nemertean Carcinonemiertes carcinophila (K6lliker, 1845). These data have revealed some facts which contribute to an understanding of the biology of both the host and the parasite. Humes (1942) described the morphology and the life cycle of Carcinonemertes carcinophila. This nemertean lives on the gills of female crabs, but becomes sexually mature only on the sponge or egg mass carried by the crab during the spawning period. During the period that the worms are on the sponge they feed on the eggs of the host. Humes stated that the worms probably return to the gills after all of the eggs of the host have hatched, basing this belief on his finding, in Louisiana, that 35% of the non-ovigerous females have worms on their gills while only 15% of the ovigerous crabs have infested gills. However, Humes was unable to distinguish nonovigerous crabs which had already spawned from mature females which had not yet laid their eggs. Humes examined 529 mature female crabs (Callinectes sapidus) during his study of Carcinonemertes at Grand Isle, Louisiana. I have data on 1011 mature female crabs in Virginia waters. As these crabs were examined primarily to determine the condition of their reproductive organs and their spawning history, these data are presented in such a way as to show the correlation between the reproductive cycles of the host and the parasite. Hard (1942) described five stages in the reproductive cycle of the mature female crab. Newly inseminated crabs, whose seminal receptacles are swollen full of the semen deposited by the male and whose ovaries have not yet enlarged, are designated Stage I. In Stage II, the seminal receptacles are no longer swollen and the ovaries are larger. In Stage III, the ovary has reached full size but the crab has not yet laid any eggs. After spawning, empty egg cases or egg stalks can be found on the swimmeret hairs, even several months after the spawning season; crabs with eggs or remnants of eggs on the swimmerets are designated Stage IV if the ovary is still large and full of eggs, and Stage V if the ovary is exhausted. In the following table, Stages II and III are combined, as are Stages IV and V, because there was no difference in their nemertean infestations.