Ptychognathus onyx   Alcock,  1900 (Crab)
Organism information awaits expert curation
Class: Malacostraca

Carapace small subcircular, almost as long as broad; flat, thin, with edges sharp. Surface smooth. Regions of carapace indistinctly marked.

Front straight, prominent, laminar, 2/5th of the width of carapace. Two post frontal tubercles present. Antero lateral sides sharp and with three sharp, acute teeth including outer orbital angle. The expodite of external maxilliped very broad, oval with smooth convex surface, in male it is more than double of ischium. Male chelipeds long, stout, smooth, inner angle of wrist produced to a long spine. Palm swollen, higher than long. A patch of thick long grey colored hairs present on the outer surface of the male palm, near the finger cleft, and extending along the fixed finger as a tuft of hair. In female the palm not hairy or swollen, but nude, its outer surface traversed by a fine ridge near the lower border, which runs to the tip of the fixed finger.

Ptychognathus onyx differs from the Ptychognathus dentata the other known Indian species, in having a long spine at the inner angle of male wrist and the patch of hairs present on outer side of palm at finger cleft, instead of on the inside of hand.

Synonym (s)
Ptychognathus onyx Alcock, 1900
Ptychognathus onyx Kemp, 1915
Ptychognathus onyx Tesch, 1918

Common Name (s)
Economic Importance and Threats

Habitat:  Estuarine


• Orissa, Chilika Lake INDIA (Record: 1914)
• Orissa, Manikpatna INDIA (Record: 12/1914)
• Andaman and Nicobar Islands, Andamans INDIA
• Bay of Bengal INDIA
• West Bengal, Palta INDIA (Record: 16/09/1936)
• West Bengal, Falta INDIA (Record: 27/03/1985)
• Orissa INDIA
• Andhra Pradesh INDIA
• Orissa, Chilika Lake (Lat: 19.46) (Long: 85.1) INDIA
• Orissa, Chilika Lake (Lat: 19.9) (Long: 85.58) INDIA
• West Bengal (Lat: 21.16) (Long: 85.83) INDIA
• West Bengal (Lat: 21.63) (Long: 89.83) INDIA
• West Bengal, South 24 Parganas INDIA
• West Bengal, North 24 Parganas INDIA

Literature Source(s)
  • Kensley, B (1981) On the Zoogeography of Southern Afrian Decapod Crustacea, with a distributional checklist of the species Smithsonian Contributions to Zoology Smithsonian Institution Press, Washington, D.C. 338 23377 Available at - NIO, RC Kochi
  • DEB, M (1995) Crustacea: Brachyura Wetland ecosystem series 1: Fauna of Chilka Lake ZSI, Calcutta 345-366 Available at - NIO, Goa
  • Society for the Management of European Biodiversity Data (2009) World Register of Marine Species (WoRMS) Available at -
  • Ghosh, SK (1995) Crustacea: Decapoda: Grapsidae Estuarine ecosystem series, Part 2: Hugli Matla Estuary ZSI, Calcutta 229-248 Available at - NIO, Goa
  • Roy, MKD and Nandi, NC (2008) Brachyuran biodiversity of some selected brackishwater lakes of India Proceedings of Taal2007: The 12th World Lake Conference 496-499 Available at -
  • Roy, MKD and Nandi, NC (2008) Checklist and distribution of Brachyuran crabs of West Bengal, India Journal of Environment and Sociobiology Social Environmental and Biological Association, Kolkata, India 5(2) 191-214 Available at - NIO,Goa
  • Roy, MK (2010) Diversity and Distribution of Crustacea Fauna in wetlands of West Bengal Journal of Environment and Sociobiology Social Environmental and Biological Association, Kolkata, India 7(2) 147-187 Available at - NIO,Goa

Page last updated on:2011-11-11

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