Slow Conduction in Solitary and Colonial Anthozoa

Abstract

The term’ slow conduction system’ has appeared many times in the recent literature on the electrophysiology of the Anthozoa (e. g. McFarlane, 1969a, 1969b, 1970, 1974a, 1974b, 1975; McFarlane and Lawn, 1972; Lawn, 1975; McFarlane and Shelton, 1975; Shelton, 1975a, 1975b, 1976; Shelton and McFarlane, 1976). In the sea anemone Calliactis parasitica, two slow conduction systems have been described — the SSI (slow system 1) and the SS2 (slow system 2) (McFarlane, 1969a). A third system, the ‘nerve net’ as described by e. g. Pantin (1935), Josephson (1966) and Robson and Josephson (1969) is also present. Slow systems have an important role in many aspects of the behaviour of sea anemones (see below) and recent work (Shelton, 1975c; Anderson and Case, 1975; Shelton and McFarlane, 1976; Shelton, 1976) indicates that they may be of general occurrence in the phylum. It is important therefore, to define what is meant by’ slow conduction’, to describe the physiological properties of slow conduction systems and, as far as possible, to try to account for these properties in terms of the actions of particular cells in the animal. This paper describes some of the properties of the best known slow conduction system, the SSI of Calliactis, and compares them with other known slow conduction systems, nerve nets and neuroid systems.