There is much confusion in the literature regarding the taxonomic status of species within the genusPerna (Siddall 1980; Vakily 1989). P. viridis can be distinguished from the other three species (P. perna, P. picta and P. canaliculus) by a few morphological characters (Siddall 1980; Rajagopal 1997). The shell of P. viridis is emerald green in colour, but the colour can vary from blue-green to brown, making it difficult to distinguish between P. viridis and P. perna. The external shell colour of P. viridis develops from green and blue-green in juvenile into brown with patches in adult (Siddall 1980). P. perna adults are usually brown with irregular areas of light brown and green.