Few investigations into the general biology of associated copepods have been made, although studies dealing with their taxonomy and structure are well documented, for example the many papers of Gotto, Bocquet, Humes and Stock. This work is an attempt to fill certain gaps in our biological information by considering the copepod Paranthessius anemoniae Claus, a cyclopoid associate of the snakelocks anemone Anemonia sulcata (Pennant). First described by Claus (1889) and later by Bocquet & Stock (1959) from Mediterranean waters, Paranthessius has only recently been reported from Irish and British waters (Gotto & Briggs, 1972; Briggs & Gotto, 1973).