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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Brachyurans > Superfamily Ocypodoidea
Semaphore crab
Ilyoplax sp.
Family Dotillidae
updated Dec 2019
Where seen? This tiny but active crab is sometimes seen in our mangroves. The common name comes from its habit of vigorously waving its pincers up and down. This is reminiscent of the Semaphore flag-waving system used by sailors in the past to send messages over long distances. In the crab, this behaviour probably serves to declare territory and to attract mates.

Features: Body width 0.5cm. Body somewhat round, eyestalks short. Pincers equal sized and rather bulbous. The White semaphore crab (Ilyoplax delsmani) changes its colour to white to communicate with other semaphore crabs. When they are resting, they turn a dull colour to blend in with the surrounding mud or sand.

Lim Chu Kang, Aug 05

Lim Chu Kang, Jan 04

Semaphore crabs on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores

Sungei Buloh, Nov 11
Photo shared by Loh Kok Sheng on flickr.

Links References
  • 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. The Raffles Bulletin of Zoology. Supplement No. 17, 31 Jan 2008. 286 pp.
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