Morphology of camouflage by encrustation in the spider crabs Schizophrys dahlak and Hyastenus hilgendorfi (Decapoda: Brachyura: Majoidea: Epialtidae) from the Suez Canal, Egypt

Abstract

ABSTRACT The spider crabs Schizophrys dahlak Griffin and Tranter, 1986 and Hyastenus hilgendorfi De Man, 1887 achieve camouflage through encrusting, allowing sessile organisms such as sponges and also masses of detritus to settle on the crabs and concealing them. Other spider crabs are decorators: they deliberately attach pieces of sponges, algae, etc. to the hooked setae of their bodies. The two species studied herein have hooked setae, but the concealing material is not in obligate association with them. We predicted that these crabs would have intricate setal morphology and unique carapace features that trapped detritus, assisted by the settlement of macro-epibionts, and aiding the crab in attaching pieces of algae, etc. Eight and 10 setal types were discovered and photographed on the exoskeletons of S. dahlak and H. hilgendorfi, respectively. The carapace of S. dahlak was characterised by surface protuberances with clusters of setae as well as patches of denticles in three distributional patterns. Hyastenus hilgendorfi had clusters of denticles located only on orbital regions. Other species of Schizophrys may have far less encrusting material than we saw in S. dahlak. We suspect that the heavy encrustation of these crabs may be related to the turbid environment in the Suez Canal.