Last week I gave you this crusty critter to identify:

It’s not the easiest mystery object, since there are around 850 species of crab, and several converge on similar forms. However, the triangular body and spindly legs meant that everyone recognised this as a species of spider crab in the Superfamily Majoidea.

Beyond that it gets harder, although there are resources out there to help. The Marine Species Identification Portal has a useful key for species that occur in the North Sea. I know that’s not always useful in these instances, but as it turns out, this particular species has a range across the East Atlantic and into the Mediterranean, including populations in the North Sea.

This little crab is Pisa armata (Latreille, 1803), which is one of several spider crabs that camouflage themselves with sessile animals and algae from their local environment, earning them the name Decorator Crabs.

Decorator crab covered in stinging hydroid polyps, which defend the crab while benefiting from food scraps and greater mobility. Image by Nick Hobgood, 2006

Bit of an obscure one for you, but Diane Barlee did figure it out on Twitter, so it was manageable. Watch out for more mysteries next week!