New distribution record of Crassostreine oyster Magallana gryphoides (Schlotheim, 1820) in Kerala, India

The Crassostreine oyster Magallana gryphoides (Bivalvia: Ostreidae) has been recorded for the first time on the Kerala coasts from Dharmadom estuary, Kannur, Kerala, India. The report indicates the range extension of M. gryphoides on the South-west coast of India. The external morphological characters were phenotypic and insufficient for species identification as it resembles Magallana bilineata. However, internal shell characters gave important information, especially the adductor muscle scar. The accurate species determination was achieved from the mitochondrial COI and 16S gene sequencing, followed by molecular phylogenetic analysis. The native oyster M. bilineata and M. gryphoides were found to co-exist in the same habitat sharing similar ecological conditions, sharing a sister group relationship

Evolution of ecophenotypic plasticity in Indian Oyster, Crasssostrea madrasensis (Preston) population from Ashtamudi Lake, Kerala, India

The Indian Oyster, Crassostrea madrasensis are abundant in the coastal waters of Tamil Nadu and Kerala. Since, they are benthic filter feeders, the external environmental conditions impose ceaseless effects on their shell affecting one or more of size, sculpture, anatomy pattern, shape and colour resulting in ecophenotypic plasticity. However, the identification of Oyster species is still based on phenotypic characters that are highly plastic. Therefore, this study aimed to investigate the phenotypic plasticity of the Indian Oyster, C. madrasensis population of Ashtamudi Lake with respect to certain ecological parameters. Individuals were collected from the barmouth and upper reaches of Ashtamudi Lake, Kerala and apparent variations were measured. Significant variations were found in the Shell colour and shell pattern. Accordingly, two morphotypes of C. madrasensis were recorded. Since, the two population exhibit remarkable differences in morphology, species confirmation was made possible using mitochondrial 16S rRNA gene. Even though 2.7% genetic distance observed between the two morphotypes of C. madrasensis is not enough to consider them as different species, it calls attention to the possibility of evolutionary divergence in the near future