''Actinia tenebrosa'', commonly known as the waratah anemone, is the most common species of

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 ...

found in the waters of eastern Australia and New Zealand (where it is known in Māori as kōtore, or kōtoretore). It is found relatively high on the seashore, in

rock pool A tide pool or rock pool is a shallow pool of seawater that forms on the rocky intertidal shore. Many of these pools exist as separate bodies of water only at low tide. Many tide pool habitats are home to especially adaptable animals that ...

s, and various cracks and shaded surfaces such as under rock overhangs in the

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

Description

When underwater, this sea anemone opens up to display numerous tentacles, arranged in three whorls. Out of water, the tentacles retract and the anemone closes to resemble a dome shaped red, crimson, brown, green or black blob of jelly, about across and high. While in a closed state, the anemone has a soft, ductile and jelly-like exterior. This species was first described in 1898 by H Farquhar who wrote "Full-grown individuals in situations well exposed to the rays of the sun have a column greenish or brownish black, and the disc and tentacles dusky crimson, while those on the undersides of overhanging stones are reddish brown or crimson, the depth of colour varying according to the amount of light which reaches them." ''Actinia tenebrosa'' is similar in form to the

beadlet anemone The beadlet anemone (''Actinia equina'') is a common sea anemone found on rocky shores around all coasts of the British Isles. Its range extends to the rest of Western Europe and the Mediterranean Sea, and along the Atlantic coast of Africa as f ...

(''Actinia equina'') of the northern hemisphere. The column has a number of iridescent blue spherules armed with

nematocyst 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 ...

Distribution and habitat

The waratah anemone is found along the coasts of southern Australia, its range extending from Perth to New South Wales. It is also found throughout New Zealand. It is found in cracks and crevices, under overhangs and under boulders on rocky shores, usually in the middle to low intertidal zone but occasionally higher up the shore.

Biology

This species is

viviparous Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the m ...

and broods its young inside its body cavity. When the offspring are well-developed they are expelled through the mouth. The juveniles often attach themselves to rocks in close proximity to the parent forming clonal clusters. When these anemones are growing alongside each other they appear to know whether or not they are closely related. If they are, they will tolerate each other's close presence, while if they are unrelated, they will attack each other. The waratah anemone can also reproduce sexually with planktonic larvae settling far away from the parent individual. It may be difficult for these juveniles to establish themselves because of resident populations of cloned individuals that are highly locally adapted.

References

{{Taxonbar, from=Q1983038 Actiniidae Animals described in 1898