509 Abstract Distribution and population density of a wood borer, Sphaeroma terebrans, in detail in relation to the prevailing ecological conditions in the intertidal subsoil of a tropical mangrove biotope is the first ever described from Cochin area in Kerala. Literature survey revealed that the species was earlier reported from the exposed and submerged wooden materials of coastal waters as well as mangrove environment of India. Occurrence of Sphaeroma terebrans in the subsoil indicated the selection of a new habitat by the organism. This species was found to have penetrated 15cm deep into the Cochin mangrove soil showing its burrowing potential and survival in that area. Monthly population density varied from 3 to 19/0.1m2. Distribution of species in the subsoil was substantially related to the high abundance of mangrove detritus and debris within the soil. The more exposed soil of the intertidal area, in connection to the tidal cycle, was well preferred as a suitable habitat by Sphaeroma terebrans. However, the species showed inconsistent distribution pattern in that area. Physicochemical factors showed no significant correlation to the distribution, substantiating the euryhaline and other tolerance behaviour of the species. Accumulation and incorporation of cellulose materials in soil pertinently render in aggregation of sphaeromids within the mangrove substratum. The great adaptability of the species to submergence of tidal water and subsequent exposure within the subsoil together with the persistent flow and prolonged standing of vegetative materials evidently supported the habitat selection of Sphaeroma terebrans and long-term survival in the distinct and dynamic mangrove littoral area.