Observations on the Diet, Feeding Mechanisms, Digestion and Food Reserves of the Entocommensal RhynchocoelanMalacobdella Grossa

Abstract

The diet and feeding mechanisms, digestive processes and nature and distribution of the food reserves of the entocommensal rhynchocoelan Malacobdella grossa (O. F. Müller) have been studied by histological, histochemical and biochemical methods.The species is predominantly an unselective microphagous omnivore and possesses two distinct feeding methods. Small particles such as bacteria, algae, diatoms and protozoa constitute the bulk of the diet and are filtered from sea water by means of a pharyngeal ciliary mechanism that does not involve the use of mucus; larger particles, mainly crustacean larvae, are caught by the proboscis and subsequently ingested intact without further treatment.Digestion occurs in the intestine and combines extra- and intracellular processes which involve mainly carbohydrases apparently secreted by gastrodermal gland cells. This emphasis on carbohydrate digestion, atypical in rhynchocoelans, can be correlated with the species diet.Fat and glycogen constitute the food reserves, with the former being the principal store and mainly deposited within the gastrodermal columnar cells.