Sediment samples were collected along a transect from 19°22'N, 58°16'E to 19°00'N, 59°00'E down the continental slope on the Oman Margin of the Arabian Sea through an Oxygen Minimum Zone (OMZ) as part of the 'Arabesque' project. Four locations from this transect were examined. Two were from within the OMZ, one was from the boundary of the OMZ and one was from deeper water which was unaffected by low oxygen concentrations. The nematodes from each replicate were examined to investigate changes in nematode biodiversity. The indicators used to assess biodiversity were abundance, taxonomic diversity, community structure, size and shape of individuals and functional morphology. The 'Arabesque' sites were compared to other locations from around the world, primarily in the deep sea, that had been sampled for nematodes. Nematode abundance was unaffected by oxygen concentration, but was most significantly correlated with food quality, measured as the Hydrogen Index. The OMZ did, however, reduce taxonomic diversity. Whilst the communities within the OMZ were more similar to each other than they were to communities outside the OMZ, it is unclear whether oxygen or depth was the controlling factor. Nematode communities from the OMZ were similar to other nematode communities at comparable depths at the generic level, but not at the family level. Nematode shape was primarily controlled by depth, with increased depth being associated with communities composed of more slender animals. This change in shape was attributed to a change in food with depth, with sediment content also potentially having an influence. On a local scale, animals were more slender in reduced oxygen environments to increase epidermal oxygen uptake. A potential new monitoring technique was discovered as nematodes found in 'disturbed' environments exhibited a reduced range of body morphologies relative to those from 'undisturbed' environments.