A new species of marine free living nematode Spinonema gracilispiculum sp. n. is described from the oxygen minimum zone of the eastern Arabian Sea (216m) margin. This new nematode species was found exclusively in the station with sandy texture and dissolved oxygen level 0.35 ml/l and are represented by only few individuals from a single location, despite analysing 288 core samples from an extensive survey along the eastern Arabian Sea OMZ region covering from 06°57'19″N to 21°30'639″N. Spinonema gracilispiculum sp. n. differs from other known species of the genus in the body length, position of the dorsal spine, contour and span of lateral alae, size and shape of spicules, number of pre cloacal setae and sexual dimorphism in presence of dorsal spine and amphideal fovea shape. This is the first record of the genus Spinonema from the Indian Ocean. A pictorial and dichotomous keys to the species of Spinonema are also provided, supplemented with comparative morphometric details of all valid species based on published information.
Keywords: Spinonema.