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| crabs text index | photo index |
| Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Brachyurans |
| Swimming
crabs Family Portunidae updated Dec 08
Where seen? Swimming crabs were commonly seen on all our shores. They particularly active at night, but are often also out and about during the day. Besides the large adults, small juvenile swimming crabs are also hidden among the seagrass and seaweed, and other nooks and crannies. These active crabs come in all kinds of colours. Some can react fiercely by waving spiny pincers, and may even give you a nip. So don't touch these crabs. Features: Body width 5-15cm. Swimming crabs are among the few crabs that are swift and agile swimmers. They usually swim sideways, but can also swim backwards and sometimes forwards. They swim with their last pair of legs which are paddle-shaped. These rotate like propeller blades when they swim. However, these crabs are essentially bottom-dwellers and don't swim about all the time. They often hide among the vegetation and slip under rocks and into other narrow crevices. Swimming crabs have a streamlined shape for racing through the water. They have long pincers armed with sharp spines to snag fish and other fast moving prey. Often, one pincer is slightly larger than the other. Here's more on how to tell apart the swimming crabs commonly encountered on our shores. Fierce Crabs: If disturbed, swimming crabs often fearlessly wave their pincers menacingly. This is not an idle threat. If you come too close, this crab might just give a good nip that draws blood! What do they eat? They eat fish, worms, other crustaceans (including other crabs), clams and snails. They may also nibble on seaweed. Swimming Babies: Like other crabs, swimming crabs can only mate when the female is moulting. Human uses: Swimming crabs are edible and enjoyed by people everywhere. In our part of the world, from Asia to Australia., the Flower crab (Portunus pelagicus) is one of the commonly eaten members of this family. Status and threats: None of our Swimming crabs are listed among the threatened animals of Singapore. However, like other creatures of the intertidal zone, they are affected by human activities such as reclamation and pollution. Trampling by careless visitors and over-collection can also have an impact on local populations. |
 Mating swimming crabs Pulau Sekudu, May 04  Eating a jellyfish Pulau Semakau, Dec 04  Tiny crab digging into a button snail Changi, Apr 05 |
Unlike other crabs, they swim very well!Swimming crabs on Singapore shores
more on how to tell apart the swimming crabs on Singapore shores
 Portunus sp. has nine 'teeth on the side of the body shell, the last one is enlarged into a long spine. |
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 Thalamita sp. has five' teeth' on the side of the body. The eyes are wide apart and the body is rather rectangular. |
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| Family
Portunidae recorded for Singapore from Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore in red are those listed among the threatened animals of Singapore from 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. *from Ng, Peter K. L. & N. Sivasothi, 1999. A Guide to the Mangroves of Singapore II (Animal Diversity)
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Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963.|
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