On the Feeding Habits and the Morphology and Mode of Functioning of the Alimentary Canal in Some Littoral Dorid Nudibranchiate Mollusca

The alimentary canal throughout the dorids is basically similar in structure and physiology, but different feeding habits result in certain modifications. Archidoris pseudoargus is a sponge-eating species which feeds on Hali-chondria panicea. The form and mode of functioning of its alimentary canal are described and compared with those in others of similar feeding habits. Food is ingested by means of the broad, many-toothed radula which acts like a rasp and a scoop. Copious secretions of mucus give protection to the gut and act as a lubricant. Digestion is at first extra-cellular, but is completed intra-cellularly. A caecum, opening from the stomach, has the principal function of compacting the sponge spicules into faecal rods, but possibly it also has an excretory r61e. The digestive gland epithelium bears three kinds of cells, of which the digestive cells are commonest. Goniodoris nodosa and G. castanea are suction feeders that eat ascidians. Like many of the smaller dorids they possess a buccal pump, which, acting in conjunction with the cutting radula, serves to ingest the semi-liquid food. The absence of particulate matter in the food is reflected in a simplification of the gut, notably in the absence of a caecum and a reduction in the secretion of mucus. Amoebocytes play an important part in digestion. The nomenclature adopted is that recently revised by Winckworth (personal communication, March 1949). A detailed account of the investigation described in the foregoing pages is being prepared for publication.