Select the search type
  • Site
  • Web




Calliactis polypus

Hermit Crab Anemone

Tara Gatehouse (2014)




Fact Sheet



Physical Description


Life History & Behaviour



Gas Exchange & Excretion


Anatomy & Physiology

External Morphology

Internal Anatomy & Physiology


Retraction-Deflation Sequence


Evolution & Systematics

Evolution with Hermit Crabs


Biogeographic Distribution

Global Distribution

Local Distribution

Conservation & Threats

References & Links

Physical Description

Body Plan

C. polypus is in polyp form, which consists of a tubular column with an oral disc,  and lacks a medusa stage, meaning it is largely sessile. It is radially symmetrical and the column is cylindrical rising from the pedal disc. C. polypus is polarized along an oral-aboral axis that parallels the environmental gradient (gravity). At the oral end of the animal, the manubrium is situated in the centre of the oral disc, enclosing the entrance to the mouth. The margin of the oral disc bears a whorl of tentacles. The mouth leads to a laterally compressed tubular pharynx that opens into the coelenteron. As the pharynx and mouth are laterally compressed, they appear to be elongated slits. The opposite ends of the slits are ciliated grooves called siphonoglyphs. Cinclides appear on the body wall, through which coelenteric fluid and acontia are released. (Ruppert E.E., 2004)

Figure 1: Close up of oral disc of C. polypus. labels: t = tentacles; o = oral discs; s = siphonoglyphs; ma = manubrium; mo = mouth; a = acontia.


The anemone ranges from 7 to 14 mm in length (column) and from 10 to 50 mm in diameter. (Fautin, 2008)


C. polypus is usually associated with pagurids. The pedal disc follows the contour of attachment substrate, usually a gastropod shell inhabited by benthic animal Dardanus sp. (Ross, 1970)  (in the case of collected specimens – pumice stone).  Usually more than one anemone is attached. Column is maroon and divided into a very short smooth scapulus and a thicker-walled scapus. The oral disc is flat, circular, and as a central mouth with two prominent siphonglyphs. The oral disc is surrounded by tentacles that are numerous, smooth and conical, with the inner tentacles being longer than the outer tentacles.  The tentacles are long, translucent brown, and have a pale base. Cinclides are located on white protuberances arranged in a single circle around the base of the column. When irritated, the retraction-deflation sequence is initiated, causing salmon-pink acontia and coelenteric fluid are discharged from the cinclides. 

Figure 2: Calliactis polypus from Henderson Rock, Moreton Island. A, two specimens on gastropod shell. B, detail of larger specimen, showing cinclides (cn) on white protuberances (pr), tentacles (t) and central mouth (m). (Fautin, 2008)

A useful resource was found to identify anemones in Moreton Bay by Fautin(2008). Click image to enlarge.