Xantho hydrophilus is a species of crab. It is yellowish-brown and grows to a carapace width of 70 mm (2.8 in). It is a nocturnal herbivore that lives in shallow marine waters from western Scotland to the Cape Verde Islands.
The carapace of Xantho hydrophilus reaches a width of 70 millimetres (2.8 in), and a length of up to 22 mm (0.9 in). The antero-lateral edge of the carapace bears five blunt lobes. It is yellowish-brown, except for the tips of the chelae, which are black. X. hydrophilus closely resembles X. pilipes, from which it can be distinguished by the absence of fringes of setae on the second to fifth pairs of pereiopods (walking legs).
Xantho hydrophilus lives under stones on sandy and stony beaches, below the intertidal zone, up to a depth of 40 metres (130 ft). It is a herbivore which feeds chiefly on various algae, and is mostly active at night.
Mating takes place in spring, and the females carry the fertilised eggs on their pleopods from March to July; the larvae can be found in the plankton over most of the summer.
Xantho hydrophilus is found from the Mediterranean Sea, the Cape Verde Islands, the Azores and the Canary Islands in the south, north to the western and southern coasts of the British Isles, reaching its northern limit in western Scotland. The populations in the Mediterranean Sea have been recognised as a separate taxon, initially as the subspecies Xantho hydrophilus granulimanus, but now generally as the species Xantho granulimanus.