Studies on gut ultrastructure and digestive physiology in Cosmocerca ornata (Nematoda: Ascaridida)

Abstract

Histological, histochemical and ultrastructural methods have been used to study gut structure and digestive physiology in Cosmocerca ornata (Dujardin, 1845). The nematode is parasitic in the small intestine and rectum of Rana temporaria, and feeds solely upon the gut contents of the host, primarily bacteria and cellular debris rather than fluid material.Only a small buccal capsule is present and no host tissue is ingested. Rigid channels at the tips of the oesophageal radii and a spiral arrangement of the corpus lumen are probably concerned in expressing any fluid in the food while retaining the particulate matter. The latter is then shredded by three large valvular flaps projecting into the lumen of the posterior oesophageal bulb. One gland is present in each sector of the bulb. There is some evidence that two secretions are produced in each subventral sector, an electron-dense one posteriorly which is released into the lumen below the valve flaps, and an electron-lucid one synthesized more anteriorly which is released in the anterior region of the bulb. Only one secretion is produced in the dorsal gland, similar to that in the anterior subventral sector, and which is poured into the lumen of the posterior corpus. The intestine is not differentiated into distinct regions and contains no gland cells. A prominent striated border of microvilli is present, varying from 25 μm in the foregut to 0·5 μm in the hindgut. They have a prominent core composed of minute fibrils and an outer glycocalyx covering.Digestion is entirely extracellular, bacteria and cellular debris in the ingesta being broken down by a C-esterase present in the oesophageal gland secretions. It is completed by a process of contact digestion with the same enzyme adsorbed on to the glycocalyx. Acid phosphatase, also produced by the oesophageal glands and present on the microvilli, may be concerned in the absorption of the resultant digestion products and any simple solutes in the food made available by host extracellular enzymes. GER and free ribosomes present in the distal regions of the gastrodermis are probably concerned in the assimilation of the absorbed materials into glycogen which is stored in large quantities in the gastrodermis.This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board.

Comparative studies on intestine ultrastructure of third-stage larvae and adults of Cystidicoloides ephemeridarum (Nematoda, Cystidicolidae)

“…The glycocalyx was shown to act as a barrier to large particles while allowing emulsified lipid, colloidal particles and substances in solution to pass freely through its meshes (Fawcett 1966). Enzymatic activity was proved on the surface of microvilli (Colam 1971), indicating that contact digestion takes place here and the nutrients are converted into a form readily absorbable by the intestinal cells.…”

“…The oral uptake of bacteria was observed in vitro. The content of the host's alimentary tract is also utilized by members of the Ascaridida (Colam 1971;Lee and Atkinson 1976), Physalopteroidea (Lincoln and Anderson 1973) and Strongyloidea. A common feature of these representatives is a buccal capsule in the shape of a cylindrical, narrow tube lined with cuticle, typical of both stages of C. ephemeridarum (see Moravec 1994;Frantova´and Moravec 2003, 2004.…”

Nematode gut peptidases, proteins and vaccination.

“…The pharynx and cloaca are, in part, lined with cuticle while the surface of the intestinal cells facing the lumen have microvilli (Bird, 1971). Oesophageal glands, one dorsal and two subventral, open into the base of the buccal capsule, while the oesophagus is separated from the intestine by the oesophago-intestinal valve (Colam, 1971). The length of the microvilli varies with nematode species from, for example, 1 µm in adult Nippostrongylus brasiliensis (Jamaur, 1966) to 5.5 µm to 7.5 µm in Haemonchus contortus (Fig.…”

The relative roles of the intestines and external surfaces in the nutrition of monogeneans, digeneans and nematodes

“…In fact, some endoparasitic helminths (e.g. the nematodes Cosmocerca ornata and Nippostrmvgylus brasiliensis) display an active (but, not necessarily circadian) migration relative to the passage of food through the host's digestive tract (Colam, 19716;Croll, 1976), and this may represent an adaptation to minimizing such temporal fluctuations.…”