''Calliactis polypus'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

sea anemone Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Hormathiidae Hormathiidae is a family of sea anemones in the class Anthozoa. Genera Genera in this family include: * '' Actinauge'' Verrill, 1883 * ''Adamsia'' Forbes, 1840 * '' Allantactis'' Danielssen, 1890 * ''Calliactis'' Verrill, 1869 * '' Cataphellia' ...

. It is usually found living on the surface of a

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard ou ...

in which a

hermit crab Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit crab, most of which possess an a ...

is living.

Description

''C. polypus'' can grow up to 8 cm (3 in) long. Several anemones can grow on one shell. The base is wide with wavy edges and pink striations and flares out over the shell surface. The column is wider at the base than further up and has pale brown and white patches and longitudinal striations. The oral disc has several whorls of long brownish translucent tentacles with paler bases surrounding the mouth.

Distribution

''C. polypus'' is found in the

Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

area and the

Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...

. It lives in the

neritic zone The neritic zone (or sublittoral zone) is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology it forms a relatively stable and well-illuminated ...

at depths down to about 25 metres (80 ft).

Ecology

''C. polypus'' lives as a

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

with several species of hermit crab including ''

Dardanus gemmatus ''Dardanus gemmatus'', the jeweled anemone hermit crab, is a species of hermit crab Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their frag ...

''. The anemone shows no inclination to attach itself to a

gastropod shell The gastropod shell is part of the body of a Gastropoda, gastropod or snail, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, and dehydration, but also serves for muscle attachment and calcium s ...

with or without a hermit crab. However the crab shows great interest in the anemone and taps and massages the base of the column with its legs until the anemone relaxes and the pedal disc becomes detached. The crab then picks up the anemone and holds it against the shell in which it is living. Both the pedal disc and the tentacles are very sticky and either can quickly form a firm attachment to the shell.The commensal association of ''Calliactis polypus'' and the hermit crab ''Dardanus gemmatus'' in Hawaii
Retrieved 2011-09-10.

References

External links

* {{Taxonbar, from=Q2435311 Hormathiidae Animals described in 1775 Taxa named by Peter Forsskål