A large testate protist, Gromia sphaerica sp nov (Order Filosea), from thebathyal Arabian Sea

The deep ocean provides a habitat for several large testate protistan taxa, e.g., xenophyophores and komokiaceans. However, testate amoebae (orders Lo busea and Filosea) have never been reliably reported from below 270 m depth . Here we describe large spherical protists, up to almost 40 mm diameter, r ecovered in box core, multicore, and epibenthic sledge samples taken on the continental slope off Oman (NW Arabian Sea) during RRS Discovery Cruise 21 1, Specimens consist of an organic envelope, with numerous tiny apertures, enclosing a mass of fine waste pellets (stercomata), On the basis of its wa ll ultrastructure (revealed by high-voltage transmission electron microscop y), this organism is identified as a member of the filosean genus Gromia, I I is described herein as Gromia sphaerica sp. nov. The wall is layered and includes the 'honeycomb membrane', a structure that is unique to this genus . The new species is the first gromiid to be reported from the deep sea. It lives between about 1200 and 1630 m below the main oxygen minimum zone, in an area where bottom-water oxygen concentrations are around 0.47 mi l(-1). The new gromiid species is clearly visible in bottom photographs taken at 1273 m (2.7 individuals m(-2)), 1318 m (2.7 indiv. m(-2)), 1624 m (17.3 ind iv, m(-2)) and 1633 m (76.5 indiv. m(-2)). They lie partly embedded in the seafloor and are sometimes grouped in twos and threes. Specimens are typica lly surrounded by an apron of lighter-coloured sediment, possibly resulting from their feeding activities. Where they lie in very close proximity, the apron around one specimen typically obscures adjacent tests. (C) 1999 Else vier Science Ltd. All rights reserved.