ABSTRACT: Sea surface and sub-surface (0–110m) water samples were collected from the Southern Indian Ocean between 39°S and 65°S (along ~48°E and 57.3°E) during the austral summer of 2010 which yielded Petasaria heterolepis. Out of the two known P. heterolepis forms, the scales with brim are observed with a size range (short and long axes length) of 1.68×1.80ym-2.17×2.27ym. The occurrence of minute pores on the scales is documented except on the brim which remains poreless. The elemental analysis of the scales revealed silica (Si) as the major constituent with the occurrence of a small peak of calcium (Ca). In spite of the presence of Ca in the scales, P. heterolepis showed lack of birefringence in the light microscopic observation. P. heterolepis is neither recognizable in the fossil record nor in the bottom sediments and shows affinity towards the extant Prymnesium neolepis recorded from off the Japan coast and Southern Indian Ocean. The present study highlights the occurrence of P. heterolepis in the open ocean regions of the Southern Indian Ocean stressing its ability to grow under diverse oceanographic conditions. The phylogenetic-molecular aspects need to be carried out which could reveal better understanding of rare Si and Ca accumulation among such haptophyte algae.