BIOLOGY OF A HOPLONEMERTEAN FROM THE BRANCHIAL CHAMBERS OF THE PINNOTHERID CRAB ZAOPS (= PINNOTHERES) OSTREUM

The pea crab, Zaops ostreum, a symbiont in the mantle cavity of the Am erican oyster (Crassostrea virginica), is itself a host to a symbiotic nemertean. This nemertean belongs to the genus Carcinonemertes, and i s similar to or possibly the same as C. pinnotheridophila, known from another sympatric pinnotherid crab, Pinnixa chaetopterana. Living in m ucous sheaths within the gill chambers of female crabs, the life cycle of the nemertean is intimately synchronized with and dependent on the crab's reproduction. A total of 138 pea crabs were collected and exam ined for nemerteans during the summers of 1965 to 1967 at Beaufort, No rth Carolina, U.S.A.; of these 97 (70%) were mature (5th stage) female crabs. Mature females harbored the nemerteans, and had a prevalence o f 39.2%. A maximum of 20 worms was found in the gill chambers of a sin gle crab, 9 of which were the red, eyeless, mature female worms, along with 11 colorless males. Worm egg sacs were attached to the pleopods of ovigorous crabs; a maximum of 293 sacs was recorded in an individua l crab with 7 mature females. At about 110 eggs per sac, this translat es to a potential production of > 32 200 nemertean larvae. Since femal e Z. ostreum may live for 2 to 3 yr and produce two broods of eggs per year (beyond the first year), the reproductive potential of the symbi onts may be even greater. Gills of crabs with more than one mature fem ale were usually covered by the worm sheaths, and were frequently dama ged (gnarled, torn, silted, etc.). The sternum of infested crabs was o ften damaged due to the projection of worm sheaths through it to the s ubabdominal region. There the egg sacs were deposited on the pleopods to develop along with the crab embryos.