Fedyaeva, M. A.; Tchesunov, A. V. (2021). Stoma and intestine ultrastructure of the marine free-living nematode Odontophora deconincki (Nematoda: Araeolaimida: Axonolaimidae). Nematology. 1-18.
The fine morphology of the buccal capsule and intestine (midgut) of the marine free-living nematode Odontophora deconincki was investigated. The cheilostome is armed with six equal claw-like odontia that can evert radially by opening the mouth. Light-refracting accessory buccal structures within the cheilostomatal cuticle alternate with odontia and consist of two elements: anterior armilloids and posterior granular armilliths. The buccal cavity (pharyngostome) is surrounded by a complex of longitudinal and oblique muscles partially attached to the cheilostome cuticle at the sites of the accessory buccal structures and enabling a wide opening of the mouth. With the described stoma condition, the nematode probably scrapes food particles from the substrate surface. In cross-section, the midgut consists of 5-7 cells that appear uniform throughout its length. An extracellular matrix (glycocalyx) over the microvillar brush varies in thickness and stratification depending on presence or absence of food content in the lumen. Abundant spherocrystals (globular inclusions with concentric striations) were present in all gut cells. No indication of endocytosis or digestive vacuoles was observed in the gut cells and extracellular digestion predominates. Most specimens had a gut content formed from a long cylinder of compressed flocculent material with some barely identifiable components and few spherocrystals expelled from the enterocytes. We assume that the nematode diet comprises a wide range of objects, mainly eukariotic epigrowth organisms, which are shorn off and scraped from the surface of sand grains and then ingested.