Parasitic Anemone

Overview

The Parasitic Anemone (Calliactis parasitica) is a marine sea anemone frequently found in a mutualistic relationship with hermit crabs. Despite its common name, it is not a parasite; rather, it is a commensal species that benefits from the mobility of its host while providing protection through its stinging tentacles.

Distribution & habitat

This species is found in the eastern Atlantic Ocean, the English Channel, and the Mediterranean Sea. While it is most commonly observed attached to the shells occupied by hermit crabs, it can also be found fixed to rocks or other hard substrates, such as the shells of living whelks.

Appearance

The anemone features a firm, cylindrical column that can reach up to 10 cm in height. Its coloration is highly variable, typically ranging from cream or buff to reddish or greyish-brown, often marked with longitudinal stripes or blotches. It possesses up to 700 slender, cream-colored tentacles. When disturbed, the anemone can expel long, white or mauve thread-like structures called acontia through small pores known as cinclides located on its column.

Feeding

Calliactis parasitica is a non-selective omnivore. It primarily functions as a suspension feeder, capturing particles from the water column, but it can also use its tentacles to gather food from the surrounding sediment. Additionally, it may opportunistically consume food scraps left behind by its associated hermit crab host.