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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Brachyurans
Rafting crab
Plagusia sp.
Family Plagusiidae
updated Dec 2019

Where seen? This bumpy crab that resembles the Sally-light-foot crab (Grapsus albolineatus) is sometimes seen on rocky shores in the North and South. Previously placed in Family Grapsidae.

Features: Body width 5-6cm. Body oval (not so circular), convex (not flat), covered with small bumps. Pincers short slender. Walking legs long fringed with short hairs, tipped with pointy claws. With these legs, the crab clings tightly so it doesn't get washed away in the waves, and can scramble quickly among slippery rocks. Mottled body and legs. Colours seen include shades of brown, blue, purple, orange.

Sometimes mistaken for the Sally-light-foot crab (Grapsus albolineatus) which has a more circular flatter smoother body.

Changi, Jul 12

Changi, Aug 12

Depression between the eyes.

Rafting crabs on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores

Changi-Loyang, Jul 20
Photo shared by Loh Kok Sheng on facebook.

Chek Jawa, Jul 13
Photo shared by Loh Kok Sheng on flickr.

East Coast Park, Jul 14
Photo shared by Loh Kok Sheng on flickr.

East Coast Park, May 21
Photo shared by Loh Kok Sheng on facebook.

Kusu Island, Aug 17
Photo shared by Marcus Ng on facebook.

Kusu Island, May 16
Photo shared by Jonathan Tan on facebook.

Raffles Lighthouse, Aug 08
Photo shared by Loh Kok Sheng on flickr.

Raffles Lighthouse, Nov 16
Photo shared by Loh Kok Sheng on facebook.

Family Plagusiidae recorded for Singapore
from Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore
+from The Biodiversity of Singapore, Lee Kong Chian Natural History Museum.
**Ng, Peter K. L. and Daniele Guinot and Peter J. F. Davie, 2008. Systema Brachyurorum: Part 1. An annotated checklist of extant Brachyuran crabs of the world.
^from WORMS

  **Family Plagusiidae (previously Grapsidae)

+Plagusia immaculata
^Plagusia squamosa=Plagusia tuberculata

Grateful thanks to Ondřej Radosta from ID Please (Marine Creatures) facebook page for helping me to understand this crab.


  • Christoph D. Schubart and Peter K. L. Ng, "On the identities of the Rafting crabs Cancer depressus Fabricius, 1775, Cancer squamosus Herbst., 1790, Plagusia immaculata Lamarck, 1818, and Plagusia tuberculata Lamarck, 1818 (Crustacea: Decapoda: Brachyura: Plagusiidae)" on The Raffles Bulletin of Zoology 2000 48(2): 327-336.
  • 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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