A substructural units of a primary biotope, defined by the generalised types of biological and physical substrate within the hard/soft/mixed categories e.g. igneous, calcareous, silts, sands, gravels, seagrasses, sponges .
- Butler, A., P. Harris, et al. (2001). An Interim Bioregionalisation for the continental slope and deeper waters of the South-East Marine Region of Australia., National Oceans Office.