Calappa granulata, the Larger Spotted Shamefaced Boxer Crab (a.k.a. the Red-spotted Shamecrab), is a marine crab species found all along the eastern coast of the Atlantic Ocean, coastal waters of Europe, the Red Sea and the entire Mediterranean Sea, thus also around the Maltese Islands.
Calappa is a genus of crabs known commonly as box crabs or shamefaced crabs. The name box crab comes from their distinctly bulky carapace, which, when at rest with the legs retracted, resembles a box. The name shamefaced is from anthropomorphising the way the crab’s chelae (claws) fold up and cover its face, as if it were hiding its face in shame.
The genus Calappa belongs to the family Calappidae, infraorder Brachyura, order Decapoda, class Malacostraca, subphylum Crustacea, phylum Arthropoda and kingdom Animalia.
The vaulted carapace of the Larger Spotted Shamefaced Boxer Crab can reach a length of 8 to 9 cm and a width of 11 to 12 cm. It is almost oval in outline, being broader than long, with the frontal edge strongly convex and ﬁnely toothed. The rear edge is weakly convex with fewer, larger teeth. The first pair of legs have strongly built pincers that have a crest on their upper side, reminiscent of a cock’s comb.
The first set of Calappa granulata ‘s walking forceps are depressed and triangular, fringed with tiny hairs which cover the eyes and hide the triangular mouth. It is believed that the hairs filter sand and other particles from water that is siphoned into the body and across the gills to extract oxygen. The line of vision is directed upwards searching for potential prey.
The colour of the Larger Spotted Shamefaced Boxer Crab ‘s carapace is pale pink, with ﬁve rows of deep red spots. The posterior part is slightly whitish. The exterior face of the cheliped propodus (major claws) is pale pink on the upper side, and white, often with some yellow tubercles, in the lower part. The legs are white on the merus and yellow on the propodus. The ungues are dark-brown.
Calappa granulata is very inactive, sometimes not moving for several days. Typically, it burrows down in the sand with just obtruding eyes, antennae and upper parts of carapace and forceps. The large forceps will form a breathing cave behind them, thus hampering any sand running in. The crab is well camouflaged in its resting place, and it is very difficult to spot as it rarely moves. When it moves, it runs upright, straightening its slim legs and is quite quick. To bury itself, it drops down and presses it forceps against the ground, pushing itself backwards into the substrate.
The Larger Spotted Shamefaced Boxer Crab feeds on molluscs and bivalves. Its large and powerful, formed forceps operate with a scissor-like action. They are well adapted to pick snails apart and are strong enough to crack the shells.
Calappa granulata live alone most of their life and only get together for mating, which is the same for all kinds of crabs. Moreover, the male Calappa granulata stays with the female while she is shedding its old shell. Apparently, this happens not to protect her, but to make sure he is close by at this time in particular. During this process, the female will be held tightly by the male until the old shell is discarded and the soft, new one appears in its place. After this ritual, the pair usually bond and mate afterward. The female then lays eggs from June to September.
The photo of this Larger Spotted Shamefaced Boxer Crab was taken at a depth of 14m at Mġarr ix-Xini on Gozo’s south coast.
Photo taken by Brian Azzopardi