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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Brachyurans
Sponge crab
Family Dromiidae
updated Dec 12
if you learn only 3 things about them ...
They use living sponges or ascidians as a disguise.
Specialised legs grip the disguise.
They tend to move slowly.

Where seen? This intriguing crab is sometimes seen on our Northern shores, in coral rubble and seagrasses areas. Those seen often 'carry' ascidians and not so much sponges.

Features: Body nearly spherical width 0.5-5cm, although sometimes larger ones are encountered. Some have a smooth body and pincers covered with fine hairs and pink tips on the pincers. Other have a very hairy body and pincers, with white tips on the pincers.

The sponge crab uses its pincers to snip out a cap out of a living ascidian or sponge to fit over its body. To grip this cap as it walks around, the crab's last pair of legs are slender, bent over its back and tipped with sharp little claws. The ascidian or sponge continues to live and grow and the crab constantly trims it to the right size. The crab's camouflage is do good that it is almost impossible to spot unless it moves. The disguise usually tastes bad and provides additional protection by discouraging predators from taking a bite out of the crab even if it is discovered. Like other crabs that rely on a disguise, it tends to move slowly.

What does it eat? The sponge crab is a scavenger, eating dead plants and animals that it comes across.


From above, looks like just
another uninteresting blob.
Chek Jawa, Aug 05


The crab is underneath!
Sponge crab babies: Females have distinctive longitudinal grooves on the underside. The eggs of some species hatch into young crabs instead of free-swimming larvae. These young shelter for some time under their mother's abdomen.

Pink tips on the pincers.

Last two pairs of legs bent over
its back to grip the disguise.

Changi, Jul 12

A 'hairy' one.

White tips on the pincers.

Sponge crabs on Singapore shores

Photos for free download from wildsingapore flickr
Distribution in Singapore on this wildsingapore flickr map

more photos of sponge crabs on Singapore shores

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

Family Dromiidae recorded for Singapore
from Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore
*from Tan, Leo W. H. & Ng, Peter K. L., 1988, A Guide to Seashore Life.
**from WORMS

  Family Dromiidae
  Cryptodromia canliculata=**Cryptodromia fallax
Cryptodromia coronata
Cryptodromia demani
*Cryptodromia pileifera
(Tunicate crab)
Cryptodromia tuberculata

Dromidia unidentata

Dromidiopsis indica
Dromidiopsis edwardsi

Links
  • Sponge Crab (Cryptodromia sp.) Tan, Leo W. H. & Ng, Peter K. L., 1988, A Guide to Seashore Life. The Singapore Science Centre, Singapore. 160 pp.
  • Sponge crabs on the Marine Crustaceans of Southern Australia page on the Victoria Museum website: brief info and photos of a crab with and without its sponge
  • Dresser crabs are abundant but hard to spot on SusanScott.net: an interesting article about Sponge crabs in Hawaii. One was found using the toxic Crown-of-Thorns seastar as its disguise and is apparently one of the few creatures than CAN actually happily eat its hat.
  • Crab with a ton of sponge on Philip Slosberg's page: a photo of a crab with a huge sponge on its back.
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. (Online PDF on the Raffles Bulletin of Zoology website).
  • 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.
  • Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore. National Council on the Environment. 163pp.
  • Ng, P. K. L. & Y. C. Wee, 1994. The Singapore Red Data Book: Threatened Plants and Animals of Singapore. The Nature Society (Singapore), Singapore. 343 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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