Abstract
A new supergiant species of Bathynomus A. Milne-Edwards, 1879 from Vietnam is described. Bathynomusvaderi sp. nov. is characterised by its wide, rectangular clypeal region with parallel lateral margins, concave distal margin, and narrowly acute apex; the distally narrowing and posteriorly curved coxa of pereopod 7; and the presence of 11 upwardly curved pleotelson spines. The new Bathynomus is the fourth species with upwardly curved pleotelson spines and the second supergiant in the South China Sea. The taxonomy of B.jamesi Kou, Chen & Li, 2017 from the South China Sea is also discussed based on a large series of specimens. Previously reported differences in body form and pleotelson spines, which suggest that there may be two forms or species, are regarded as intraspecific variation for the time being. The contemporary culinary trend and fishing of Bathynomus in Vietnam, which have contributed to this discovery, are also discussed.