Gyrineum natator is a large, robustly sculptured species, easily distinguished from all its congeners by being the largest species of the genus, by its low varices, by its thin shell, by its more strongly shouldered whorls, producing a stepped outline to the varices, and by its dark brown to dark olive green-brown coloration, uniform in some specimens, and in others consisting of dark nodules on a paler ground (pale brown, yellow, or white). The aperture is white, with smoother lips than in most other species. The protoconch resembles those of other species with high whorl numbers, and has 2.6 whorls . H 48.6, D 28.2

Throughout the western and central Indian Ocean, as far south as Beira, Mozambique, recorded from the Gulf of Arabia (BOSCH et al. 1995: 95); common along the southern coast of Asia, frequently seen in collections from India. Hong Kong and Singapore; and south to Indonesia. The eastern and southern limits are poorly known; not recorded from Mauritius or Reunion by DRIVAS & JAY (1988), nor from the Philippine Islands by SPRINGSTEEN & LEOBRERA (1986). A lot in NZGS from "Sulu Sea" is as likely to be wrongly localised as it is to indicate an eastern limit just reaching into the southwestern Philippines. Recorded from New Guinea(?) by HlNTON (1978: 30. fig. 12) but no specimens from Australia exist in Australian museums. The easternmost Indonesian specimens in AMS are from Bali (C60883) and the Moluccas Islands (C34885).