Sea Anemones: a brief note:

by Andy Horton

Hormathia (Photograph by Andy Horton)SEA ANEMONES

Sea Anemones belong to the phylum of animals known as the Cnidaria, from the cnida or sting capsule that are present in this major group of animals that also include the corals, jellyfish, hydroids, medusae, and sea fans.  Sea anemones, corals and their allies form the class known as the Anthozoa.

 Structure and Form

Sea anemones are primitive animals consisting mostly of a column with a single opening, the mouth, used to ingest food and expel wastes. Stinging organelles are found throughout the animal, in the tentacles, and in some species in stinging threads (acontia), and beads (acrorhagi).

Beadlet Anemones (photograph by Andy Horton)Beadlet AnemoneSagartia troglodytesBeadlet AnemoneSagartiogeton undatusGem AnemoneSagartia troglodytesAnthopleura balliiDahlia Anemone

Tentacles are found in groups of six in many families, with the largest usually on the inside, with increasing numbers near the parapet of the column. The flattish area on top around the mouth is called the disc, or oral disc. The upright column can vary in shape. Wart-like protuberances called verrucae are noticeable in rows on the column in some species. Other anemones possess small suckers, but these need to be observed under a magnifying glass. Anemones are attached to rocks by the basal disc.

 Anemone bodies are divided into two primary layers known as the ectoderm (or epidermis) for the exterior, and the internal endoderm (or gastrodermis) connected by the mesoglea tissue. The internal gastric centre is also known as the cavity.
 Beadlet Anemones, Actinia equina, are common  on all rocky coasts around Britain.


Sea Anemones often remain in same place for several days, weeks or even months. However they can move around in two ways:


Sea Anemones are probably distasteful to most fish and are ignored by crabs in British seas. However, the Grey Sea Slug, Aeolidia papillosa, feeds exclusively on sea anemones, and the shallow water fish, the Tompot Blenny, Parablennius gattorugine, demonstrates an eagerness to decimate an anemone population in aquaria as the first choice of food.

Grey Sea Slug feeding on a Beadlet Anemone.

Photograph by Andy Horton.


Sea Anemones are not plants but predatory animals. The sting capsule in the tentacles and other parts of the sea anemone each contain a coiled hollow filament, usually barbed and containing venom. They are used to catch smaller organisms, for defence, and to fight territorial battles. These capsules can be seen under the microscope and their mechanism is arguable the fastest action in the whole of the animal kingdom. When triggered by touch, the capsule turns inside out and drives the filament into its prey discharging its venom.

The tentacles manipulate the food to the single opening for digestion. Wastes are expelled through the same opening. Sea anemones breathe through the general body surface. There are no special organs.

Tricks to feed difficult sea anemones in aquaria

I recommend the following book:

Functional Biology of Sea Anemones  1991
JM Shick
The first comprehensive treatment of the sea anemones for fifty years, this book presents an integrated synthesis of their biology.
It emphasizes their physiological ecology, evolutionary biology and biological interactions with other taxa, and it includes a wide-ranging bibliography.

424 pages, 87 illus.

Publisher: Chapman and Hall. Date of publication 1991.
ISBN 0-412-33150-0


BMLSS  Book Hunt Page

Biomar Sea Anemones and other Anthozoa
Cnidaria (BMLSS)
Cnidaria Discussion Group
Cnidaria Web Site (World)
British Sea Anemones Database (under construction)
European Register of Species: Actiniaria
Worldwide Sea Anemone DataBase (External Site)
Diagram of a Sea Anemone
Hydrozoan Society (
Jellyfish Page (BMLSS)
New Anemone Page (under construction)
References to British Sea Anemones
Reproduction in British Sea Anemones
Zooxanthellae in Cnidarians



IMAGES  on flickr

Images of British Cnidarians
Cnidarians of the World
Sea Anemones

British Coelenterate Society

1999 Meeting

Species of Sea Anemone , Order: Actiniaria, recorded at Shoreham-by-Sea and Worthing:

Actinia equina          Common
Actinia fragacea        Occasional
Anemonia viridis        Frequent

Urticina felina         Occasional
Metridium senile        Frequent
Sagartia troglodytes    Common
Cereus pedunculatus     Rare
Actinothoe sphyrodeta   Rare
Sagartiogeton undatus   Occasional

Anthopleura ballii      Rare
Diadumene cincta   Offshore, 3 metres depth  (Photographs)
All from personal observation (Andy Horton)
Haliplanella lineata
From Report in Widewater Lagoon.
Edwardsia ivelli
From Report in Widewater Lagoon.
(NB. In some reports the grid ref is printed incorrectly).
October 1997. A recent search of Widewater Lagoon failed to discover the miniature anemone Edwardsia ivelli.
(Red-speckled) Pimplet Anemone

Actiniaria Species List

Anthozoa (US External)
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Actinia equina