Three different morphotypes of an intertidal macrobenthic brachiopod, Lingula anatina have been found to inhabit in three contrasting intertidal mudflats (based on different soil textures and vegetations) in an ecotone, the confluence of Subarnarekha estuary (21°35’48” Northern Latitude
and 87°27’17” Eastern Longitude) with the Bay of Bengal, India. The species under study is very unique in respect of size, shape, texture and colour of shell and possesses longer lophophoral cavities, shorter
ventral canals, long pedicle, well-developed posterior adductor muscles etc., showing phyllogenetic relationship with mesozoic lingulids. Gut content analysis and assessment of bioturbatory activities have established the roles of the studied species towards ecosystem functioning which also displayed distinct seasonal fluctuation of population density (0- 2986±123.12 Nom-2), biomass (0-1287.88±93.69 gm-2 and size class (0 -13.32 cm) in relation to the prime physicochemical parameters such as salinity, pH, temperature, nutrients etc. of both soil and interstitial water during the period of July 2009 to June 2011. Different statistical tools such as ANOVA,Duncan’s Test, Regression and Correlation analyses
have revealed the impact of tidal inundation and exposure along with other ecological variables in determining the occurrence, distribution and population fluctuation of this faunal component.

Lingula anatina, Subarnarekha estuary,ecological variables, population.