Opelet or Snakelocks Anemones – Anemonia viridis (Forskål) – exhibit quite a bit of variation in form and colour. Generally they are described as having “a smooth column, usually wider than high, up to 50 mm in diameter. Disc wide, with up to 200 long and sinuous tentacles; the tentacles rarely retracted. Column and acrorhagi (a ring of specialised warts) brownish, tentacles brown, grey or bright grass green, usually with purple tips. Contains zooxanthellae. On the shore in pools and other places open to the light, and down to about 20 m” (Hayward and Ryland 1998).
The bright green tentacle colour is caused by the tiny algae (zooxanthallae) that live within them. It is said that these organisms live in the specimens of anemone that live in well lit areas while the grey-brown anemones, without the symbiotic algae, live in areas without much light. However, that cannot be true because grey-brown and green individuals can live side by side. In the images below, Snakelocks Anemone (3) and (4), in the top left corner of the photographs you can see a plain grey-brown Snakelocks Anemone next to the featured green specimen with the pink- purple tips. And the grey-brown specimens in Snakelocks Amenone (5) – (8) were found within a few metres of the green ones.
The literature says that the tentacles of the Snakelocks Anemone are rarely retracted or withdrawn. This could be a bit of a problem for the anemone when the tide goes out. All the green anemones shown in this post were photographed in very shallow water pools in which the columns of the animals were flattened or compressed against the rock floor of the pool to ensure that the whole animal with its fully extended tentacles remained beneath the water surface. The brown specimen attached to a loose rock was fully exposed to the air and had partially retracted its tentacles – the first time I had seen this – presumably to minimise dehydration.
Typically, the Snakelocks Anemone has slender, delicate tentacles with fine gently tapering tips. The anemones from Lyme Regis in Dorset (1-4 & 8) have this characteristic. Recently, on a trip to the Worms Head Causeway, Gower, South Wales, I noticed some specimens with tentacles that were markedly stouter than usual. Additionally, a large number of the tentacles had blunt tips or had one or more constrictions towards the end. I think that the difference in tentacle shape is due to the particular conditions of the habitat. The Worms Head Causeway is a very high energy environment where the impact of wave action is accentuated; while the habitat provided by the shore at Lyme Regis tends to be a less extreme environment. The different shapes of the Worms Head Snakelocks Anemone tentacles could be the direct result of physical damage.
P. J. Hayward & J. S. Ryland (Eds) (1995 reprinted 1998), Handbook of the Marine Fauna of North-West Europe, Oxford University Press, pp 120-125.
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