The Larval Development of Dissodactylus Primitivus Bouvier, 1917 (Brachyura: Pinnotheridae) Reared in the Laboratory

Dissodactylus primitivus is a small pinnotherid crab occurring symbiotically on the spatangoid urchin Meoma ventricosa. The complete development from hatching to the first crab instar is described and illustrated. The larval development consists of a prezoeal stage lasting about 5 min, followed by three zoeal stages with a mean duration of 1, 2.1, and 2.7 days, respectively. The megalopa can be reached by the sixth day (mean 6.8), the first crab instar by day 12 (mean 15.3). The zoeae of D. primitivus are very similar to those of D. crinitichelis, the only other species in the genus for which the complete larval development is known. There are some differences in size, duration of instars and chromatophores on the first abdominal somite. Later zoeal stages also show minor differences in setation. The megalopa and first crab instar exhibit several diagnostic features, including size, developmental time, chromatophore pattern and setation, which makes it possible to distinguish these stages from those of D. crinitichelis in the absence of their respective host echinoids.