Common Spider Crab

• defensaIt decorates its own shell with scraps of seaweed and small fixed invertebrates, a living camouflage it renews from time to time.
• It has a terminal moult: on reaching maturity it moults for the last time and never grows or changes its shell again for the rest of its life.
• It makes seasonal migrations of tens of kilometres, and groups have been seen advancing in single file along the seabed.
• It migrates en masse and in single file. In autumn the spider crabs gather and travel tens of kilometres across the seabed towards deeper water, in columns that have been filmed off Atlantic coasts.
• And they pile up to moult: they form heaps of tens or hundreds of individuals, in which the soft, freshly moulted animals are protected at the centre by the hard-shelled ones.
• It is a decorator crab: it covers its carapace with algae and sponges held on by hooked bristles, a camouflage it maintains throughout its juvenile life.
• It stops growing on reaching maturity: its last moult is the final one, so an adult spider crab never moults again and its carapace becomes covered with epibionts over the years.
• That makes it possible to estimate a specimen's age from the wear and encrustations on its carapace.
• It is one of the most prized species in Galician shellfishing, and its fishery is regulated by minimum size and closed seasons.

Skeleton type

Invertebrate - chitin exoskeleton (crustacean)

Habitat and environment

Sand, gravel and rock bottoms, from 5 to 120 m

Sources consulted: Wikipedia (es): Maja squinado

Best time: Autumn and winter, when it moves inshore