The waters around the UK are home to a variety of crabs of all shapes and sizes. They are one of those creatures that are very distinctive, so most people on seeing one can identify them as a crab. Selsey, West Sussex is famous for its edible crab, you may have seen it being served in restaurants and on fish counters, and it forms an important part of Selsey’s Fishing Heritage. In this article we will be looking at some small crabs called Sponge or Scorpion Spider Crabs – Inachus spp. There are in fact three different species which are very hard to tell apart.
Crab are crustaceans, which means they wear their skeleton on the outside and have a segmented body, jointed legs for movement and shed their shell as they grow. Sponge crabs are a smaller species, with a triangular body and long slender legs, reaching a maximum of 10cms across the spread of the legs and body. Close up images show that they can have almost a bucked tooth/small fang look to them. They are frequently covered with sponge, another marine creature, that grows on the body and legs, it appears that they can place the sponge themselves. This sponge tends to cover up those details that you need to tell the different species apart, so most recordings tend to be not at the species level. There is a clue that is not on the crab itself, Inachus phalangium likes to hang out around snakelocks anemones, sitting either in the tentacles or sheltering under the anemone column.
Fully covered in sponge and algae growth they can be a little tricky to spot, it took me a good while to see my first. However, once you see them, they are everywhere and almost every snakelocks has at least one close by. They live commensally with the anemone, benefiting from the protection that the tentacles offer from other creatures and feed on bits of food the anemone drops, but do not harm the anemone in the process.
The ones I have seen are often covered with pale yellow or orange sponge. One memorable sighting was when I came across about six of them in a line, as you progressed along the line each one was covered in more sponge until they look seriously beefy! To see them for yourself I would recommend SCUBA, on big tides you might find one in good sized rock pool but they like to be deeper, I would say if you see a snakelocks look for a crab…how I found my first!
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