Description of Pseudocapillaria (Discocapillaria) trilobularis n. sp. (Capillariidae) and redescription of Heliconema alatum (Majumdar, 1965) (Physalopteridae), two nematodes parasitising synbranchiform fishes in India.

One new and one already known species of nematodes are described based on specimens collected from synbranchiform fishes of the River Ganga, India, in 2021 and 2022. Pseudocapillaria (Discocapillaria) trilobularis n. sp. (Capillariidae) from the intestine of cuchia Monopterus cuchia (Hamilton) (Synbranchidae) is mainly characterised by the presence of the large ventral postcloacal lobe in the male, the spicule length 351 µm, eggs size 60-69 × 30-36 µm (with protruding polar plugs) and by the body length (male 10.50 mm, females 11.02-12.44 mm). It is the fourth species of this genus recorded from fishes in India. The species Heliconema alatum (Majumdar, 1965) (Physalopteridae) is resurrected. This nematode is redescribed from specimens collected from the intestine of zig-zag eel Mastacembelus armatus (Lacepède) (Mastacembelidae). The examination by SEM revealed some previously not reported morphological features in this nematode species, e.g., the presence of cephalic papillae or a lateroterminal depression and two inner flat dorsoventral teeth on each pseudolabium. Based on these findings, H. monopteri Moravec, Chaudhary & Singh, 2019 is considered a junior synonym of H. alatum.