''Anthopleura stellula'' 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 ...

Actiniidae Actiniidae is the largest family of sea anemones, to which most common, temperate, shore species belong. Most members of this family do not participate in symbioses with fishes. Three exceptions are the bubble-tip anemone (with anemonefish and ...

. It was first described in 1834 by Wilhelm Hemprich and Christian Gottfried Ehrenberg as ''Actinia (Isacmaea) stellula.'' It is found in the Indian Ocean and the Red Sea, and is unusual among sea anemones in that it can divide itself in two transversely.

Biology

''Anthopleura stellula'' is unusual among sea anemones in that it can divide by transverse fission. This is not a common method of

asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...

among these sea anemones but tends to occur as a reaction to stress, such as when an anemone is experiencing a lowering of the salinity. The fission involves the animal forming a transverse constriction before dividing in two, the oral portion growing a new pedal disc and the basal portion growing a new oral disc and pharynx. There are a few other sea anemones such as '' Gonactinia prolifera'' that can divide in this way, and all are rather small, primitive sea anemones with simple internal structures. Internal reorganisation often starts before the fission process commences. During the fission process, an indentation occurs halfway down the column, new tentacles begin to develop below the constriction, and the two portions separate. Research has shown that a decrease in salinity encourages fission while an increase prevents it happening. When ''A. stellula'' was placed in an aquarium with the gem anemone ''

Aulactinia verrucosa ''Aulactinia verrucosa'', the gem anemone, is a species of sea anemone in the family Actiniidae. It is found on rocky coasts in the northeastern Atlantic Ocean, North Sea and Mediterranean Sea. Description ''Aulactinia verrucosa'' has a cylindr ...

'' and the salinity was reduced, the fission of ''A. stellula'' induced fission in ''A. verrucosa'', even though that species never spontaneously undergoes fission in other circumstances. It is thought that ''A. stellula'' produces "fission substances" when the salinity falls, and that these can circulate in the water and affect other sea anemones.

References

{{Taxonbar, from=Q2305022 Actiniidae Animals described in 1834 Taxa named by Wilhelm Hemprich Taxa named by Christian Gottfried Ehrenberg