Creature of the Month

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Scorpion Spider Crab
Inachus dorsettensis














This small, triangular, crab disguises itself from predators with tiny pieces of living sponge and seaweed. It sticks these among the hooked setae (bristles) on its back as camouflage.  

 You will often find it in the tentacles of the snakelocks anemone - as in our picture - another strategy to evade its predators. Research on a very similar species, Inachus phalangium, has found that he crab can walk through the anemone without the anemone trying to eat it.

Inachus only leaves the anemone during night-time to feed, and when moulting. It does not always return to the same anemone but sometimes migrates to a different area to find a mate or more food.  

The Scorpion spider crab takes food into the anemone; the anemone takes advantage of this and may grab the food from the crab for itself. However, the anemone may also collect more food than it can eat quickly, thus benefitting the crab.

The crab's legs are very long and slender but the claws are rather big and sturdy. It is difficult to distinguish from I. phalangium, but I.dorsettensis's carapace (upper shell) is not as pointed between the stalked eyes. 

Inachus dorsettensis grows to just 3 cm across and lives from 4 to 300 m in the coastal waters of Europe, including around the British Isles and the Mediterranean. It has also been recorded in South Africa.

Reprinted with permission:
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