Familia Actiniidae

Goldfuss, 1820

Thenaria with the base forming a well-defined adherent disc with a limbus; not more than one tentacle arising from each endo- and hexocoele; tentacles arranged normally, in cycles, more than 36 tentacles in adults. Mesenteries not differentiated into macro- and microcnemes; acontia absent. Sphincter rnuscle is endodermal, strong, weak, or occasionally absent. Column often divided into scapus and capitulum, with parapet and fosse, often bearing verrucae and/or acrorhagae.

In some actiniid genera the scapus bears numerous hollow, wart-like verrucae, which are frequently arranged in distinct longitudinal rows; they may be adhesive, having particles of gravel or other debris stuck to them, but in some species they are apparently non-adhesive and never have gravel, etc. stuck to them. At the upper margin of the scapus, mounted either on the parapet or in the fosse, a single encircling series of acrorhagi may occur. These are hollow warts, similar to verrucae although usually more protruberant, which contain numerous holotrichous nematocysts, they function as organs of aggression being used in intraspecific combat. Although the distinction between verrucae and acrorhagi is important in defining some genera, the British actiniid species can be easily distinguished without the need to determine this distinction by examining the nematocysts.

Actiniids are mostly typical shore-dwelling anemones having a worldwide distribution. Many species live on exposed rocky shores where strong wave action is prevalent, a habitat which few other anemones prefer.