A new species of Polyipnus (Teleostei : Stomiiformes) from the western Indian Ocean, with comments on sternoptychid ecology

Polyipnus limatulus is described based on material collected in the Gulf of Aden and immediately adjacent areas of the northwestern Indian Ocean. Thes e collections were made during midwater fish surveys conducted from three v essels, R/V Beinta (1987), R/V Malcolm Baldridge (1995), and R/V Tyro (1992 ). Like other species in this genus P. limatulus appears to occur in associ ation with the continental slope and/or various types of sea floor rises. P olyipnus limatulus shares certain apomorphic characters with the P. spinosu s species group; among these are a multispinose posttemporal, and the occur rence of numerous spine-like denticles on the modified scales covering many of the ventral photophores. These denticles are lacking on the ACB photoph ore scales, a character which distinguishes the new species from a putative ly closely related species, P. asper (eastern Indian ocean). Polyipnus indi cus (western Indian Ocean) has somewhat similar scale denticulation but has a relatively unmodified parietal, among other differences. The new species was found to occur in relatively warm, saline, low oxygen water associated with Red Sea outflow, whereas the other Polyipnus species collected during the R/V Tyro survey, P. omphus Baird, 1971 was collected in the colder, le ss saline, higher oxygen water associated with the Somali Current.