Isognomon isognomum   (Linnaeus,  1758) (Oyster)
Organism information awaits expert curation
Class: Bivalvia

Image copyrights: G. & Ph. Poppe

Size: Maximum shell height 15 cm, commonly to 10 cm; length 13.42-40.34 mm

Color: Outside of shell bluish or brownish purple to almost black, often paler to whitish umbonally. Interior porcelaneous and similarly colored on non-nacreous area, nacreous area much paler, with bluish purple hue.

Shell relatively high and narrow in outline, with undulating commissure and strong posteroventral elongation. Shape often very irregular, due to the confined space in which the shell grows and to the effect of repair. Dorsal margin long and straight to slightly arched, more or less strongly expanded posteriorly in a wing-like ear that increases with growth and may attain a size double the length of shell. Anterior margin elongated, markedly sinuous dorsally and extending a little or not at all forward of umbones. Posterior margin concave near the posterior ear, then more or less parallel to anterior margin. Ventral margin roughly rounded. Umbones small, pointing at anterior end of dorsal margin. Outer surface with irregularly concentric lamellate processes, often encrusted with marine growths and corroded towards the umbones. Ligamental area with numerous transverse grooves (more than 20 in large specimens). Nacreous area of the inner side of shell more or less expanded ventrally, its margin often poorly defined.

Synonym (s)
Isogonum isognomum (Linnaeus, 1758)
Isognoma lignea Lightfoot, 1786
Isognomon brevirostre Link, 1807
Ostrea isognomum Linnaeus, 1758
Isogonum isognomum Satyamurti, 1956
Isognomon isognomon (Linnaeus, 1758)
Isogonum gnomon Roding, 1798
Isogonum norma Roding, 1798
Ostrea isogonum Linnaeus, 1767
Perna aquila Clessin, 1890
Perna attenuata Reeve, 1858
Perna avicularis Lamarck, 1819
Perna canina Lamarck, 1819
Perna femoralis Lamarck, 1819
Perna fimbriata Reeve, 1858
Perna flava Clessin, 1890
Perna isognomon var. brachyptera Martens, 1894
Perna isognomon var. obliqua Martens, 1894
Perna isogona Bosc, 1801
Perna novohollandiae Clessin, 1890
Perna patibulum Reeve, 1858
Perna planulata Clessin, 1890
Perna rollei Clessin, 1890
Perna rudis Reeve, 1858
Perna tranquebarensis Leach, 1815
Perna vespertilio Reeve, 1858
Perna vulsella Reeve, 1858

Common Name (s)
Economic Importance and Threats
Importance:  Commercial
(Collected for food and marketed.)



• Orissa, Off Ganjam Coast INDIA
• Tamil Nadu, Pamban INDIA
• Tamil Nadu, Shingle Island INDIA
• Andaman and Nicobar Islands, Andamans INDIA
• Tamil Nadu, Mandapam INDIA
• Tamil Nadu, Mandapam INDIA

Literature Source(s)
  • Rao, GC (1990) Present status of the sea cow, Dugong dugon Journal of Andaman Science Association 6 185-189
  • Poutiers, JM (1998) Bivalves FAO species identification guide for fishery purposes. The living marine resources of the western central Pacific. Volume 1: Seaweeds, corals, bivalves and gastropods FAO, Rome 1 686 pp Available at -
  • Society for the Management of European Biodiversity Data (2009) World Register of Marine Species (WoRMS) Available at -
  • Rao, NVS; Rao, KVS and Maitra, S (1991) Marine molluscs State fauna series 1: Fauna of Orissa Zoological Survey of India, Calcutta Part 3 1-175 Available at - NIO, Goa
  • Poppe, GT and Poppe, P (1996) Conchology, Inc. Conchology, Inc. Available at -
  • Sundaram, KS; Sarvesan, R; Mohamed, KH and Shanbhogue, SL (1969) Catalogue of molluscs, prawns, stomatopods and marine algae in the reference collections of the central marine fisheries research institute Bulletin Of Central Marine Fisheries Research Institute CMFRI, Cochin 9 1-52 Available at -

Page last updated on:2011-03-14

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