 The juveniles of "X. poressa" are cryptically coloured as camouflage among the epibionts on the leaves of "Posidonia" with a variable carapace colour, which can be yellowish, reddish, brown, or dark grey with patches of another colour, usually white.The pereiopods are usually banded with dark brown or black bands alternating with white or translucent stripes or spots, although the fifth pereiopod is brighter and often unmarked.The adults are uniformly dark grey in colour and they leave the seagrass beds for more open, rocky substrates.