Description: This sea anemone has an adherent base and a fairly tough and leathery column, without tubercles and not divided into regions. Acontia are emitted readily from the lower part of the column. The tentacles are moderate in length, up to about 700 in number. The diameter of the base measures up to 80mm and height to 100mm. The column is yellow/buff in colour, mottled and spotted with brown or reddish. The markings usually form vertical stripes, often with black, red or purple spots in addition. The lower column has vertical, pale yellow stripes. The disc and tentacles are cream, rarely pink or orange, the tentacles usually with inconspicuous broken brown lines.

Habitat: Usually found in association with hermit crabs (Pagurus bernhardus in Britain) attached to the shell; occasionally on living whelks (Buccinum undatum) or on shells or stones. Exclusively sublittoral in occurrence but sometimes washed up on the shore during storms.

Distribution: Common on south coasts of Britain but scarce in Ireland. Reported north to the Bristol Channel and the southern Irish Sea; common in Tralee Bay but otherwise absent from Ireland; southwards to the Mediterranean.

Similar Species: Unlikely to be confused with any other species, very different from the other British hermit crab commensal Calliactis palliata.

Key Identification Features:

• Usually associated with hermit crabs.
• Very numerous tentacles with only a faint pattern.
• Acontia readily emitted.

Distribution Map from NBN: Calliactis parasitica at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Calliactis parasitica at iNaturalist World Species Observations database.

WoRMS: Calliactis parasitica at World Register of Marine Species. Accepted name: Calliactis parasitica (Couch, 1842). AphiaID: 100946.

Classification: Biota; Animalia; Cnidaria; Anthozoa; Hexacorallia; Actiniaria; Enthemonae; Metridioidea; Hormathiidae; Calliactis