These are actually two animals!
In the picture you see a hermit crab with an anemone attached to its house. This is a special crab and a special anemone (Adamsia palliata) that live together in what we call a symbiosis.
It is a way of life where two species live close to each other, and one or both of them benefit from it. In this case, both the crab and the anemone get an advantage from living literally on top of each other - which we again call mutualism. The anemone obtains food by picking up the food scraps left by the crab. In return, the hermit crab receives protection from the anemone by scaring away predators by shooting out purple stinging threads from its body when it senses disturbance. This may be because the crab produces fear hormones that the anemone responds to.
But what happens to the anemone when the hermit crab has to change its shell?
A few weeks ago, we put out a video showing a hermit crab changing its shell. Hermit crabs have to do this regularly as they grow. With this symbiosis, the anemone probably responds to chemical signal substances secreted by the crayfish and lets go of the old shell, so that the crayfish can attach itself to the new one. The anemone will also grow larger over time and could eventually cover the entire shell.
Did you also know that these species are common along the Norwegian coast? They can be found from shallow water down to a depth of 60 metres.
