Complete Larval Development of Clypeasterophilus Stebbingi (Decapoda: Brachyura: Pinnotheridae) and a Comparison with Other Species within the Dissodactylus Complex

Clypeasterophilus stebbingi is a small pinnotherid crab living as an ectosymbiont on the Atlantic sea biscuit Clypeaster subdepressus. It is the only known species of Clypeasterophilus to develop through four zoeal stages before metamorphosis to the megalopa. Eggs were incubated by females for 12-14 days at 28°C. Beginning with the first zoea, mean duration for each stage was 3, 2, 3 and 4 days, with the first megalopae appearing 10 days after hatching (mean 12). All larval stages are described and illustrated in detail, with special attention to the identity, morphology and distribution of setae. Zoeae of Clypeasterophilus can be separated from those of Dissodactylus by the absence of dorsolateral spines on the second abdominal somite. Within Clypeasterophilus, C. stebbingi zoeae differ from those of C. rugatus in the shape of abdominal somites and telson, and in the setation of the basipodite of the first maxilliped. Between megalopae of the two species there are differences in the chromatophore pattern, setation and cheliped morphology. Morphometrically, zoeal stages of C. stebbingi have a smaller carapace than comparable stages of C. rugatus, whereas the megalopa of C. stebbingi is much wider.