Joris van Alphen Photography

Into the Wild

Photo of the Month: Porcelain Crab

Posted May 9, 2013. Filed under: Biology, Nature, Photography, Underwater. One comment.

Porcelain crab (Neopetrolisthes oshimai, Neopetrolisthes maculatus) in carpet sea anemone (Stichodactyla mertensii).

Like anemone fish, this porcelain crab (Neopetrolisthes oshimai) grows a layer of mucus that protects it from the poisonous sting of its host anemone (Stichodactyla mertensii). Ternate, Indonesia.

Only three centimeters in size, this beautiful porcelain crab is seeking shelter between the tentacles of a carpet sea anemone. Like anemone fish, it has a special trick to keep safe from the poisonous sting of its host.

You see, sea anemones feed in much the same way as jellyfish. In fact, the two are closely related. Their tentacles are covered with tiny poisonous harpoons that fire on touch, capturing and paralyzing prey that swim into them, as well as keeping predators at bay. It’s a nice trick, but of course there is a catch—without some way to prevent it from stinging itself, tentacles bumping into each other would constantly trigger those little harpoons. And so the sea anemone coats itself in a mucus that effectively carries a message: This is me, don’t sting!

However, some animals have found a way to exploit the sea anemone’s defense against itself. Most famous for this are of course anemone fish, but there are many other small ocean creatures that use the same tactic. The porcelain crab is one of them. It coats itself in sea anemone mucus, tricking the sea anemone into confusing the porcelain crab for itself. This way the porcelain crab is safe from the sea anemone, but more importantly, hiding between its host’s poisonous tentacles, it is safe from other predators. It can go about its business feeding without too much fear of becoming a meal itself.

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