ИСТИНА

Nematode stomas vary broadly in shape, but the gut structure looks the same. Here, we want to show variety of gut ultrastructure in species of feeding types according to Wieser (1953). The species are Oxystomina sp. (selective deposit feeder with a tiny stoma), Paramonhystera filamentosa (non-selective deposit feeder with a medium-sized unarmed stoma), Paracanthonchus caecus (epigrowth feeder with medium-sized stoma armed with tooth, denticles and other sclerotized structures) and Halichoanolaimus robustus (predator with a large stoma equipped with teeth). All these species consume their food in different ways. While Oxystomina sp., P. filamentosa, and H. robustus swallow their food, P. caecus crushes it. As a result, some species swallow liquid matter whereas other species feed on coarse food. Due to this difference, we can see various gut structure. Oxystomina sp. and P. caecus gut cells have not sparse located microvilli and amorphous extracellular layer (glycocalyx). P. filamentosa and H. robustus gut cells have thick multilayered glycocalyx (as protection from coarse food) and closely located microvillie. In conclusion, there is no direct link between feeding type and gut structure, but we can relate the last one with feeding manner and consistency of swallowing food. This project was financially supported by the Russian Foundation for Basic Researches, grant № 20-54-56038. ‒ 1Lomonosov Moscow State University Marine Research Centre, Moscow, 119992, Russia. E-mail: mariaf92@mail.ru. 2Department of Invertebrate Zoology, Faculty of Biology, Lomonosov Moscow State University, Russia. E-mail: avtchesunov@yandex.ru.