LIFE-HISTORY AND BIOLOGY OF THE OYSTER CRAB, PINNOTHERES OSTREUM SAY AAGE M0LLER CHRISTENSEN 1 AND JOHN J. McDERMOTT Oyster Research Laboratory, Rutgers University, N. J. Agricultural Experiment Station, Birahe, A r . /. While the adult female of several species of the pea crab, Pinnotheres, has been known since ancient times, it is not clear when the first male was observed and de-scribed. The earliest reference available to the present authors was found in a paper by Thompson (1835). He describes the male of P. pisum as being firm in texture, with compressed, hairy appendages and of flatter form and much smaller size than the (adult) globu-lar, soft-shelled female. Such hard-shelled P. pisuni were generally all thought to be males until Orton (1921) demonstrated the existence of hard-shelled females, which except for differences in the genital apertures and the pleopods proved to be indistinguishable from the males. However, hard-shelled females \vere known in at least four other species of Pinnotheres prior to 1921 (Rathbun, 1918). Pos-sibly, Thompson (1835) was also aware of this in P. pisum as he states, "For a considerable time the young females are scarcely to be distinguished from the males, and in this stage both differ so much from the adult, as to render it probable that they have often been taken for individuals of different species, . . ." Orton (1921) was the first to find a soft-shelled male, which except for the same characteristics as mentioned above resembled the immature female of similar size. A few years later, Atkins (1926) studied and described all the growth stages of P. pisum found in Mytilus ediilis in English waters. As Orton, she regarded the hard-shelled crabs as free-living, invasive crabs, a point of view which the author later abandoned (Atkins, 1954, 1955). Hence the hard-shelled stage of both sexes was designated as Stage I. In the female, four more stages were described, the fifth and last stage being the mature crab. In the male, only the hard-shelled stage was described, no reference being made to Orton's discovery of a soft-shelled specimen. It was stated, however, that a few abnormal males were found. Soft-shelled males were found also by Mercier and Poisson (1929), who stated that they were abnormal due to the influence of an entoniscid parasite. Later Atkins (1933) disproved this statement and expressed the hope of discussing the matter in a later paper as she still considers these males as abnormal. Stauber (1945) found and described similar growth stages in P. ostreum from the American oyster, Crassostrea virgmica. He therefore followed Atkins (1926) in designating the hard-shelled stage as the first (invasive) stage, which in the fe-male is succeeded by four more stages as in P. pisum. Stauber also found a num-ber of soft-shelled males, evidently corresponding with the finds of P. pisurn men-tioned above. With some reservation, he referred these males to a second stage 1 Present address : Det marinbiologiske laboratorium, Helsing^r, Denmark. 146
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