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Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Infraorder: Brachyura
Family: Varunidae
Genus: Chasmagnathus
De Haan, 1833 [1]
Species: C. convexus
Binomial name
Chasmagnathus convexus
(De Haan, 1835) [1]
Synonyms [1]
  • Ocypode (Chasmagnathus) convexus De Haan, 1833
  • Helice spinicarpa H. Milne-Edwards, 1853

Chasmagnathus convexus is a common mud-flat crab of the family Varunidae, which is endemic to East Asia.[2][3] In Japan, this crab is commonly called hamagani. This crab has two forms that differ in color; one is olive green and the other is purple.[2] Differences in diet are believed to be responsible for the color variation between the two forms. C. convexus is large, relative to related crabs, and can reach 4.5 to 5 centimetres (1.8 to 2.0 in) wide across its carapace.[4] It is predominantly nocturnal.[2]


  1. ^ a b c Peter K. L. Ng; Danièle Guinot; Peter J. F. Davie (2008). "Systema Brachyurorum: Part I. An annotated checklist of extant Brachyuran crabs of the world" (PDF). Raffles Bulletin of Zoology. 17: 1–286. Archived from the original (PDF) on 2011-06-06. 
  2. ^ a b c Hsi-Te Shih; Hiroshi Suzuki (2008). "Taxonomy, phylogeny, and biogeography of the endemic mudflat crab Helice/Chasmagnathus complex (Crustacea: Brachyura: Varunidae) from East Asia" (PDF). Zoological Studies. 47 (1): 114–125. 
  3. ^ Katsushi Sakai (ed.). "Chasmagnathus convexus". Crabs of Japan. Retrieved January 16, 2009. 
  4. ^ Hitoshi Miyasaka; Motomi Genkai-Kato; Yukiko Goda; Koji Omori (2007). "Length-weight relationships of two varunid crab species, Helice tridens and Chasmagnathus convexus, in Japan" (PDF). Limnology. 8 (1): 81–83. doi:10.1007/s10201-006-0195-8.