SCUBAHUB
The mention of a Montagu ’ s crab after a dive or rock pool ramble sometimes draws a blank expression but , as soon as you say ‘ the crab that looks like a bodybuilder ’, there is usually a spark of recognition ! Somehow , the big heavy claws and the deep grooves in its carapace give exactly that impression . It is those grooves or ‘ furrows ’ and the lack of a ‘ pie-crust ’ edging that makes Montagu ’ s crabs easy to distinguish from edible crabs , the other common heavily-built crustaceans . Edible crabs are also generally much less belligerent when discovered but , unlike edible crabs , the fierce-looking Montagu ’ s crab is interestingly reported to be a seaweed-consuming vegetarian .
I haven ’ t covered the Montagu ’ s crab in Critter before because , while I come across them a lot when exploring rocky shores , I very rarely saw them when snorkelling or diving . That seems to have changed here in the last couple of years and I now regularly see that distinctive face , positioned between strong claws , peering back at me when I shine my light into a crevice on the shallow Devon reefs where I spend so much time underwater . Is this a real expansion of their range , or have I just got better at spotting them ? Yet again , this is a question that as an individual I cannot answer and where an organised observation and recording scheme like Seasearch is so valuable and powerful .
The occupation of crevices on our local reefs by Montagu ’ s crabs is of particular interest to me because of my fascination ( some would say obsession !) with tompot blennies . Feisty and territorial tompots seem to have no problem in driving velvet swimming crabs and edible crabs out of their home crevices , using a cunning mixture of bites at the crabs ’ vulnerable parts and shoving with their muscular tails . Montagu ’ s crabs seem to be made of sterner stuff however , and I have yet to see a tompot blenny evict one . For example , one favourite hidey-hole that has had a succession of tompot ‘ owners ’ over the years is now just home to a Montagu ’ s crab wedged tightly into the very back of the crevice . Such losses of long-held tompot territory are very rare and they aren ’ t usually even put out by a conger eel moving in next door !
The closely related Risso ’ s crab has less pronounced ‘ furrows ’ on its shell , so it looks less ‘ muscular ’ than Montagu ’ s crab . Both species can be found together on the shore but , underwater , I have only seen Risso ’ s crabs on sand or maerl seabeds rather than on rocky reefs . Risso ’ s crab is usually prettily patterned or paler than the typically chestnut-coloured Montagu ’ s crab but , as always , colour can be deceptive . The best distinguishing feature is that Risso ’ s crab has dense hair on most of its legs , while the back legs of Montagu ’ s crab bear relatively few bristles , just like those of a body-builder ! �
Montagu ’ s crab in a rocky crevice , it has the typical brown colour with black-tipped claws
CRITTER CONFIDENTIAL
Montagu ’ s ( or furrowed ) crab Xantho hydrophilus
......................................... Risso ’ s ( or lesser furrowed ) crab Xantho pilipes
This heavyset character is one of the UK ’ s more obscure crab species , but Paul Naylor has a solid method for identifying it
Risso ’ s crab showing off its very hairy legs
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