The marine nematode genus Bathylaimus Cobb, 1894 (Enoplida: Tripyloididae Filipjev, 1918) is widely distributed and occurs usually in sandy sublitoral shallow marine habitats. Over 40 species have been described so far.
The head region is typical for this genus and composed of a mouth opening surrounded by 3 incised wide rounded lips. The cephalic setae are often jointed. The buccal cavity is usually very large in most species and composed of a broad anterior sclerotized part with a dorsal tooth and a much smaller posterior weakly sclerotized part complemented with two smaller teeth. The amphid is rounded and spiral shaped and situated at or the just behind buccal cavity level. The tail in both sexes is relatively short, conical and usually curves towards the ventral side. The gubernaculum is large and well developed compared to the spiculum.