Evidence for Direct Development in Meiopriapulus fijiensis (Priapulida)

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Abstract
Studies of preserved specimens from a single population of Meiopriapulus fijiensis indicate that, unlike all other species of the phylum Priapulida, this species has no loricate larval stage in its life history. Females commonly contain two or as many as eight oocytes. One oocyte matures at a time, reaching an approximate diameter of 250 mu-m. This is nearly three times the diameter reported for other priapulid species for which data are available. Evidence suggests that the embryo is brooded by the female. A postembryonic stage, lacking anal hooks and functional introvert, of nearly the same linear dimension as the oocyte, is released from the female urogenital pore into the infralittoral fringe zone of coarse sand and shell-hash where it develops into a juvenile slightly larger in size. The juvenile is similar to the adult, but it has only 13 anal hooks instead of the adult number of 25 and lacks obvious indication of maturing gonads. Juveniles undergo a series of molts. The adult condition is reached by a length of approximately 800-mu-m, at which size gonads are first observable in whole mounts. Adults continue to molt and attain a maximum trunk length of 2.15 mm.

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