title: The second species of Gromia (Protista) from the deep sea: its natural history and association with the Pakistan margin oxygen minimum zone.
abstract: We describe a gromiid protist Gromia pyriformis sp. nov., from bathyal depths on the Pakistan margin (NE Arabian Sea), an area characterised by a well-developed Oxygen Minimum Zone (OMZ). The new species is smaller (length usually <1 mm) than the only other described deep-sea gromiid species (Gromia sphaerica) or the well-known coastal species Gromia oviformis. Its identification as a gromiid is based on the test-wall ultrastructure. This includes (i) an outer wall (165-300 nm thick) limited by an electron-opaque layer and perforated by pore structures which typically extend through its entire thickness, and (ii) inner "honeycomb membrane" structures which form a discontinuous sheet (18-20 nm thick) lying parallel to the outer wall. An outermost glycocalyx (approximately 75 nm thick), not observed in other gromiid species, is also present and imparts a finely granular appearance to the outer test surface, as seen by Scanning Electron Microscopy (SEM). Numerous rod-shaped prokaryotes are attached to the exterior of the glycocalyx. Gromia pyriformis sp. nov. typically occurs above the sediment-water interface, attached to the large arborescent foraminiferan Pelosina sp. It is confined to a very narrow bathymetric zone (approximately 1000 m water depth) in the lower portion of the OMZ, where bottom-water oxygen concentrations are approximately 0.2 ml l(-1).
authors.affiliation: Southampton Oceanography Centre, Empress Dock, European Way, Southampton SO14 3ZH, UK. ang@soc.soton
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Gooday
authors.forename: Samuel S
authors.initials: SS
authors.lastname: Bowser
mesh_terms: D000818:Animals; D056890:Eukaryota / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D009792:Oceans and Seas; D010100:Oxygen / Q000032:analysis / Q000378:metabolism*; D010154:Pakistan
chemical_list: D010100:Oxygen