Cloak Anemone

Overview

The cloak anemone is a distinctive sea anemone known for its obligate mutualistic relationship with the hermit crab Pagurus prideaux. It typically lives attached to the gastropod shell inhabited by the crab, often enveloping the shell entirely with its wide, convoluted base.

Appearance

This anemone features a beige or white column frequently marked with characteristic oval-shaped lilac or reddish-purple spots. Its oral disc and tentacles are generally white or pale, often positioned beneath the crab. When threatened, the anemone can discharge numerous stinging threads, known as acontia, which are typically purple or white in color.

Biology & behavior

The relationship between the cloak anemone and its host is a classic example of mutualism. The anemone provides the crab with protection through its potent stinging cells, while the crab provides the anemone with mobility and access to food scraps. As the hermit crab grows, the anemone may secrete a chitinous material called a carcinoecium, which extends the shell to accommodate the crab. When the crab needs to change shells, the anemone can detach and relocate to the new home, likely in response to chemical signals.