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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Brachyurans > Family Portunidae
Ridged swimming crab
Charybdis natator*
Family Portunidae
updated Oct 2016
Where seen? This swimming crab is not often encountered, under stones on sandy shores.

Features: Body width 5-7cm, to 17cm. Body somewhat fan-shaped with 6 spines on the sides. The eyes not very far apart. Between the eyes there are 8 small rounded lobes. Last pair of legs are paddle-shaped and rotate like boat propellers, so the crab swims well in all directions. It is a fully marine crab and cannot live long out of water. Body usually plain beige, covered with fine hairs which traps sediments. Legs and pincers reddish brown with dark coloured bumps, black tipped with blue spots at the base of the 'fingers' of the claw.

Sisters Island, Jan 12

Lazarus Island, Apr 12
Photo shared by Loh Kok Sheng on his blog.

Changi, Apr 05

6 spines on the body side.

*Species are difficult to positively identify without close examination.
On this website, they are grouped by external features for convenience of display.

Ridged swimming crabs on Singapore shores

Photos of Ridged swimming crabs for free download from wildsingapore flickr

Distribution in Singapore on this wildsingapore flickr map


Changi, Apr 13
Photo shared by Marcus Ng on flickr.

Changi, Apr 13
Photo shared by Marcus Ng on flickr.


Tanah Merah, Mar 13

Photo shared by Loh Kok Sheng on flickr.

Kusu Island, May 14
Photo shared by Rene Ong on facebook.

   Links References
  • Lim, S., P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life and Times of Labrador Beach. Division of Biology, School of Science, Nanyang Technological University & Department of Zoology, the National University of Singapore. 160 pp.
  • Jones Diana S. and Gary J. Morgan, 2002. A Field Guide to Crustaceans of Australian Waters. Reed New Holland. 224 pp.
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