Histological, histochemical and ultrastructural methods have been used to study gut structure, digestive physiology and food storage in the free-living marine nematode Pontonema vulgaris (Bastian, 1865).
Examination of the gut contents indicates that the nematode feeds by drawing in mud and silt and digesting bacteria and any other organic materials present.
The gut consists of mouth, buccal capsule, suctorial oesophagus, intestine and rectum. The buccal capsule contains three interradial teeth, through which open the ducts of the oesophageal glands. These glands lie posteriorly in the interradial sectors of the oesophagus, with a single acidophilic gland cell in the dorsal sector and two cells, one acidophilic and one basophilic, in each of the two subventral sectors. The oesophageal region shows no enzymic reactions histochemically but extracts show esterase activity, and it is suggested that one gland cell type produces an enzyme precursor and the other an activator, the two secretions yielding an active enzyme when mixed on discharge.
The intestinal wall contains glandular cells, whose secretions show carbonic anhydrase activity and are believed to be acidic, and columnar cells concerned with absorption. Both possess microvilli and there is some evidence to suggest that the columnar cell may normally develop into the secretory type which after functioning in a merocrine fashion eventually dies and is extruded into the gut lumen.
Production of secretion within the glandular cells is of the usual pattern, involving the granular endoplasmic reticulum and Golgi complexes.
All the intestinal cells contain pigment granules, which show reactions for ferric and ferrous iron but whose precise nature and function remain unknown.
Digestion is extracellular and with test meals of blood lipid is formed as an end-product within the columnar intestinal cells. Esterase, believed to originate in the oesophageal glands, is concerned in digestion, as also are the products of the glandular cells of the intestine.
Food reserves consist of glycogen and fat, deposited in the intestinal wall, lateral chords and eggs; glycogen also occurs extensively in the body wall musculature and in the oesophagus between the muscle bands, and lipid in the interstitial zone of the testis.