Digestion in Sea Anemones

A sea anemone, normally a passive-looking animal, reacts to suitable food,.. stuffs by a series of fairly complicated activities. When its tentacles encounter solid food there is, first of all, a discharge of cnidae, which poison living prey and adhere to the food mass. These cnidae are independent effectors, responding directly to external excitation (Pantin, 1942). Next, the tentacles clasp the food and bend towards the mouth; they push the food into the mouth, and the pharynx draws it down into the coelenteric cavity where it is digested (Pantin & Pantin, 1943). The food bolus lying in the coelenteric cavity gradually disintegrates, and the particulate and soluble products of digestion are absorbed. The indigestible residue is finally expelled from the mouth. Bath,am & Pantin (1950) have recorded the phasic activities of Metridium following feeding: these include elongation of the column, peristaltic movements and, finally, defaecation and shrivelling after about 48 h. The faecal pellets which are extruded are covered with thick mucus. According to Yonge (1931, 1937, 1954), some preliminary digestion of protein takes place extracellularly in coelenterates, whereas' the digestion of carbohydrates and fats, and. the final degradation of proteins are all carried out intracellularly. Previous workers have had difficulty in demonstrating an extracellular protease in actinians, since' fluid drawn from the coelenteron usually possesses little or no proteolytic activity (Mesnil, 1901; Bodansky, 1924). Many lines of evidence show, however, that extracellular digestion does take place (Boschma, 1925; Yonge & Nicholls, 1930; Krijgsman & Talbot, 1953). There is, seemingly, a paradox between the low proteolytic activity of coelenteric fluid, and the demonstrated efficacy of coelenteric digestion, and some experiments were made to investigate certain aspects of digestive secretion in sea anemones.