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''Actinodendron arboreum'', commonly known as tree anemone or hell's fire 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 sea anemone in the
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Actinodendronidae. It is native to the Indo-Pacific where it grows at depths of down to . Most sea anemone species are harmless to humans, but ''A. arboreum'' is highly venomous and its sting can cause severe skin ulcers (as also suggested by its alternative name, hell's fire anemone).


Description

The oral disc of ''Actinodendron arboreum'' has stripes that radiate from the mouth, and can reach a diameter of 10 to 20 centimetres. The column is elongated when expanded; it has a fairly small pedal disc and is thicker at the distal (upper) end. The tentacles are colourless, around 10 to 20 centimetres long and ramify fractally, being subdivided into branches and branchlets which makes the whole head of tentacles resemble a
broccoli Broccoli (''Brassica oleracea'' var. ''italica'') is an edible green plant in the cabbage family (family Brassicaceae, genus ''Brassica'') whose large flowering head, stalk and small associated leaves are eaten as a vegetable. Broccoli is cla ...
. The tentacles grow in whorls as the animal enlarges; the first whorl is six tentacles followed by further whorls of six, twelve and twenty-four tentacles. The first and third whorls of tentacles are endocoelic (set between the
mesenteries In zoology, a mesentery is a membrane inside the body cavity of an animal. The term identifies different structures in different phyla: in vertebrates it is a double fold of the peritoneum enclosing the intestines; in other organisms it forms com ...
in the column interior) and the second and fourth are attached marginally. The sea anemone is well-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 c ...
s which are of varying lengths, the ones in the central region of the tentacles being least variable.


Biology

Breeding in ''Actinodendron arboreum'' takes place when gametes are shed into the body cavity and passed out into the
water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...
. After fertilisation, the
planula A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species and also in some species of Ctenophores. Some groups of Nemerteans also produce larvae that are very similar to the planula, which ...
larva forms part of the
plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...
before settling on the seabed, undergoing metamorphosis and developing into a juvenile sea anemone.


References

{{Taxonbar, from=Q3333973 Actinodendridae Animals described in 1833 Taxa named by Jean René Constant Quoy Taxa named by Joseph Paul Gaimard Cnidarians of the Indian Ocean Cnidarians of the Pacific Ocean