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 seen on our Northern shores, in coral rubble and seagrasses areas. Those seen often 'carry' ascidians and not 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.

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.

• Photos for free download
• Map of sightings in Singapore

• 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.

• 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.
• 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.