Did you know that some animals get by with a little help from their “friends”? Certain species of marine hermit crabs have a symbiotic relationship with sea anemones, meaning they mutually use each other for their own benefit. Riding along the hermit crab shell, sea anemones get the opportunity to be mobile and have more access to planktonic food, while the the hermit crab gains protection from predators. But what happens when a hermit crab grows and needs a bigger shell? Some hermit crabs will poke the sea anemones until they relax and the hermit crab is able to transfer the anemone to its newer, bigger shell. However, some sea anenomes, like the cloak anemone (Adamsia palliata) grows as the hermit crab (genus: Pagurus) grows by wrapping itself around the hermit crab, and secreting a chitinous shell over the current hermit crab shell.

Fact and sketch by Karli Chudeau

Source: Dunn, D.F., Devaney, D.M., & Roth, B. (1981). Stylobates: A shell-forming sea anemone (Coelenterata, Anthozoa, Actiniidae). Pacific Science, 34(4), 379-388.