''Cerianthus membranaceus'', the cylinder anemone or coloured tube anemone, 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 ...

of large,

tube-dwelling anemone Tube-dwelling anemones or ceriantharians look very similar to sea anemones but belong to an entirely different class of anthozoans. They are solitary, living buried in soft sediments. Tube anemones live inside and can withdraw into tubes, which ...

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 ...

Cerianthidae Cerianthidae is a family of tube-dwelling anemones in the order Spirularia of the subclass Ceriantharia. Genera The World Register of Marine Species includes the following genera in the family: * ''Anthoactis'' Leloup, 1932 * ''Apiactis'' Bened ...

. It is native to the Mediterranean Sea and adjoining parts of the northeastern Atlantic Ocean.

Description

''Cerianthus membranaceus'' is a large, tube-dwelling anemone. The oral disc can have a diameter of up to . There are two whorls of tentacles, amounting to about two hundred tentacles in all. Those in the outer whorl are long and slender and armed with

cnidocyte A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this ce ...

s (stinging cells) and are used for catching prey. Tentacles in the inner whorl are shorter and function to transfer captured food to the central mouth. The tentacles are sometimes banded and come in an array of colours; white, yellow, orange, green, brown, blue, black, purple and violet. The colour of the inner whorl often contrasts with that of the outer whorl. The column of this tube anemone secretes

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

in which is embedded a unique type of cnidocytes that mesh together to form a fibrous structure. Sand and other particles adhere to this and it forms a leathery, protective tube up to in length. There is no pedal attachment and the lower end of the tube is buried in the soft substrate. The tube is open at the base which allows for escape of water when the animal retreats into the tube.

Distribution and habitat

''Cerianthus membranaceus'' is found on the seabed in shallow water in the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...

, the northern

Adriatic Sea The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to t ...

and the northeastern Atlantic Ocean, its range extending as far north as Britain. It occurs on sandy or silty substrates where its tube is buried vertically in the sediment. In the Mediterranean, it principally occurs in areas with high levels of organic matter, such as in zones of pollution off

Marseille Marseille ( , , ; also spelled in English as Marseilles; oc, Marselha ) is the prefecture of the French department of Bouches-du-Rhône and capital of the Provence-Alpes-Côte d'Azur region. Situated in the camargue region of southern Franc ...

, where it is present at high densities throughout the year.

Ecology

The tentacles of ''Cerianthus membranaceus'' do not retract, but the whole animal can retreat into its tube. As it does so, some of the tentacles grip the rim and pull the tube closed behind it, effectively making it disappear from view. The tube is normally a permanent home, but if the anemone is disturbed from below, as by a burrowing

sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...

, it can eject itself from its tube, move to a new location and secrete a new tube. ''C. membranaceus'' feeds on small fish and

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

ic organisms which it catches with its tentacles. It is a

protandrous hermaphrodite Sequential hermaphroditism (called dichogamy in botany) is a type of hermaphroditism that occurs in many fish, gastropods, and plants. Sequential hermaphroditism occurs when the individual changes its sex at some point in its life. In particular, ...

, starting life as a male and becoming a female later. The gametes are liberated into the sea and after fertilisation, the developing

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e drift with the plankton for a long time before settling on the seabed and undergoing

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

into juvenile polyps. The tube is used as a refuge by many

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 ...

organisms, especially

polychaete worms Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are m ...

and

shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

s. The horseshoe worm, '' Phoronis australis'', often attaches itself to the outside of the tube. There may be twenty to fifty horseshoe worms associated with one tube anemone. The lifespan of ''C. membranaceus'' in the wild is not known, but some individuals have been occupants of a tank in Naples Aquarium for more than fifty years.

References

External links

* {{Taxonbar, from=Q876386 Cerianthidae Animals described in 1791