Morphological variations in blood cockle Tegillarca granosa (L, 1758) populations collected from the south-east and south-west coasts of Bangladesh

Morphology helps in studying the external features of an individual, including the size, shape, structure of the animals and in determining the evolutionary relationships among organisms. Current study was undertaken to investigate the morphological variations between the two populations of blood cockle, Tegillarca granosa collected from the south-east (west coast of Maheshkhali Island, Cox’s Bazar; S1) and south-west (Jamuna River Estuary near Ishawrypur, Shemnagar, Shatkhira; S2) coasts of Bangladesh. Samples were drawn from the intertidal region during low-tide by hand-picking with the aid of local people in March 2020 from both sites. Fifteen primary parameters, and 27 secondary parameters obtained from the ratios of different primary parameters were studied to compare the values between the two populations. Out of 15 primary morphological parameters, there was no significant difference (p>0.05) between the populations. Among the 27 secondary morphological parameters, only 4 parameters were significantly different (p<0.05) between the two populations. The statistically different parameters were shell length (SL)/wet tissue weight (TWW), shell height (SH)/wet tissue weight (TWW), shell thickness (ST)/wet tissue weight (TWW) and condition index (CI). The ratios of shell dimensions and wet tissue weight were significantly higher (p<0.05) in S2 when compared with S1 indicated that S1 population could be more economically viable due to their relatively higher edible meat content. The CIs were significantly higher (p<0.05) in S1 population than the CIs of S2 population. The values of CIs reflected that S1 population had better health condition than S2 population. The ratios of different shell measurements did not vary significantly implied that both populations were homogenous in size, shape and structure. Morphological analyses of different populations of T. granosa revealed that habitat could play a vital role in morphological variations.