Hydractinia echinata

Hydractinia echinata is a colonial marine hydroid which is often found growing on dead, hermit-crabbed shells of marine gastropod species. This hydroid species is also commonly known as snail fur, a name which refers to the furry appearance that the hydroids give to a shell.

In the northwestern Atlantic, these hydroids are especially common on the outside of shells that are occupied by the flat-clawed hermit crab.