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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Brachyurans > Family Parthenopidae
Common elbow crabs
Rhinolambrus pelagicus
Family Parthenopidae
updated Oct 2016
if you learn only 3 things about them ...
They are tiny well camouflaged crabs. That's why we should avoid stepping areas thick with seaweeds and seagrasses.
Their 'elbows' are often much longer than their bodies!
To see one, look carefully at every bit of 'rubbish'.

Where seen? These tiny, slow-moving crabs look like bits of dirt or junk among seaweeds. Look very carefully to find them. Elbow crabs are commonly seen on our Northern shores, among seagrasses and seaweeds.

Features: Body width 1-2cm. An obvious feature of the crab (once you can actually see the crab) is its elbows: highly elongated large pincers that stick way out from the sides of its body. The upper finger is moveable and curved towards the immobile lower finger. Males may have larger pincers than females. The thin walking legs are small and have pointed tips. Body somewhat triangular or pentangonal, with eyes at the pointed tip. The crab's body and claws may be fuzzy or bumpy and coloured the same as mud or sand. Some have fluffy growths and other encrustations, even keelworms growing on the body and arms.

The pincers are large, relative to the crab, and look like they can do some serious damage to small prey. The inner surface of the pincers have a row of coloured bumps and spots that are probably used to startle predators.

Elbow crabs commonly seen on our shores could belong to various species including Parthenope sp. and Rhinolambrus sp. They are difficult to identify in the field.

Elbow crab food: The elbow crab eats worms and small snails and clams.

Status and threats: Some of our elbow crabs are listed among the threatened animals of Singapore. Like other creatures of the intertidal zone, they are affected by human activities such as reclamation and pollution. Trampling by careless visitors also have an impact on local populations.

Pincers many times longer than its body.
Changi, May 06


Mama crab with egg mass on her abdomen.
Pulau Sekudu, Jun 05

Just moulted.
Pulau Ubin, May 03

Changi, Aug 09

Pair about to mate?
Cyrene Reef, Jun 09

Common elbow crabs on Singapore shores

Photos of Common elbow crabs for free download from wildsingapore flickr

Distribution in Singapore on this wildsingapore flickr map


Beting Bronok, Jun 10
Photo shared by Loh Kok Sheng on his blog.

Sentosa, Jul 16
Photo shared by Marcus Ng on facebook.

Kusu Island, May 16
Photo shared by Loh Kok Sheng on facebook.


St John's Island, Feb 13
Photo shared by Loh Kok Sheng on his blog.

St John's Island, Feb 11
Photo shared by Loh Kok Sheng on his blog.

Acknowledgement
Grateful thanks to Ondrej Radosta for identification help with these crabs.

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.
  • 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.
  • Davison, G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened plants and animals of Singapore. Nature Society (Singapore). 285 pp.
  • Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore. National Council on the Environment. 163pp.
  • 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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