Notes on the Unusual Megalopae of the Ghost Crab Ocypode quadrata and Related Species (Decapoda: Brachyura: Ocypodidae)

摘要

The postlarval stage, or megalopa, of Ocypode quadrata (Atlantic Ghost Crab) has distinctive morphological characteristics, with large size being its most recognizable character. Nevertheless, there is little biological or ecological information on this critical stage in the crab's life cycle. Over a 20-year period (1980-2000) of field work, only five specimens have been collected incidentally along the sandy beaches of southern New Jersey, near the northern limit of its geographic range. Megalopae were obtained via seine, hand net, and sediment core samples from September 6 to October 6, even though some of the locations were sampled throughout the year. Mean carapace width (CW) and length (CL) for the five megalopae were 4.85 +/- 0.59 mm by 6.14 +/- 0.68 mm, respectively; CW ranged from 4.01-5.43 mm and CL from 5.18-7.01; mean CW/CL ratio was 0.790 +/- 0.023. Carapace dimensions of New Jersey specimens were compared with megalopae recorded in the literature from the shores of Long Island, NY and North Carolina, as well as data from two eastern Pacific species, Ocypode gaudichaudii and O. occidentalis. Morphology of the megalopa appears to be adaptive for survival through metamorphosis into the first crab stage. Recruitment of O. quadrata to sandy beaches in the northern part of its range is probably in the fall.