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.

[4] The larvae of X. poressa go through four zoeal and one megalopal stages, which are typical of most of the related species of crabs in the subfamily Xanthinae.

[5] Juveniles live in Posidonia meadows until their last moult, when they migrate to the nearest rocky substrate.

[3] In the Black Sea, X. poressa is common near the shoreline at depths less than 1 m; it is mainly found stones on substrates of pebble and crushed rock; it is rare on the other substrates and may occur down to 15 m in depth.