Feeding and digestion in Dinophilus gyrociliatus (Annelida: Archiannelida)



The littoral archiannelid Dinophilus gyrociliatus Schmidt 1857 is microphagous and feeds on bacteria, protozoa, unicellular algae, diatoms and organic detritus. Two types of feeding mechanisms are used and both are relatively unselective. In the first, suspended particles brought to the head in water currents set up by the beating of transverse ciliated bands are trapped in mucus and swept laterally and ventrally on to the under surface of the head, where further ciliary activity conveys them posteriorly to the mouth.

In the second feeding method the proboscis dislodges microscopic food from the sub-stratum and freed particles are collected by ventral cilia and passed into the mouth.

Mucus discharged into the mouth facilitates ingestion and other non-mucoid secretions are poured on to the food as it passes from the oesophagus into the proventriculus where it accumulates. The proboscis is then periodically thrust up the oesophagus to drive the accumulated material onwards into the stomach.

Digestion is entirely extracellular. Proteolysis initiated in the stomach by endopeptidases secreted by acidophilic glands in the stomach wall is completed in the posterior region of the stomach and in the intestine by exopeptidases produced by other components of the gut epithelium. Acid phosphatase activity is present throughout the gut epithelium at all times, irrespective of the nutritive state of the animal, but alkaline phosphatase can be demonstrated only whilst food is present in the gut. This enzyme is confined to a thin distal band below the cilia of the stomach and intestine, and reaches maximum activity in the intestinal wall 18 h after feeding, indicating that it is concerned with absorption of the products of digestion.

Fat deposits occur in the stomach wall and constitute the main food reserve. Amyloid granules are laid down subepidermally in the anterior region of the body and there is some evidence that these too are utilized during periods of food shortage.