Biology of a hoplonemertean from the branchial chambers of the pinnotherid crab Zaops (= Pinnotheres) ostreum

Abstract

The pea crab, Zaops ostreum, a symbiont in the mantle cavity of the American oyster (Crassostreavirginica), is itself a host to a symbiotic nemertean. Thisnemertean belongs to the genus Carcinonemertes, and issimilar to or possibly the same as C. pinnotheridophila,known from another sympatric pinnotherid crab, Pinnixachaetopterana. Living in mucous sheaths within the gillchambers of female crabs, the life cycle of the nemertean isintimately synchronized with and dependent on the crab's reproduction. A total of 138 pea crabs were collected andexamined for nemerteans during the summers of 1965 to 1967 atBeaufort, North Carolina, U.S.A.; of these 97 (70%) were mature(5th stage) female crabs. Mature females harbored thenemerteans, and had a prevalence of 39.2%. A maximum of 20worms was found in the gill chambers of a single crab, 9 ofwhich were the red, eyeless, mature female worms, along with 11colorless males. Worm egg sacs were attached to the pleopods ofovigorous crabs; a maximum of 293 sacs was recorded in anindividual crab with 7 mature females. At about 110 eggs persac, this translates to a potential production of >32 200nemertean larvae. Since female Z. ostreum may live for 2to 3 yr and produce two broods of eggs per year (beyond thefirst year), the reproductive potential of the symbionts may beeven greater. Gills of crabs with more than one mature femalewere usually covered by the worm sheaths, and were frequentlydamaged (gnarled, torn, silted, etc.). The sternum of infestedcrabs was often damaged due to the projection of worm sheathsthrough it to the subabdominal region. There the egg sacs weredeposited on the pleopods to develop along with the crabembryos.