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Hermit crabs Suborder Anomura Hermit crabs are common everywhere on Chek Jawa. They come in all sizes from tiny to large, and live in all kinds of shells. Living in a shell: Hermit crabs are not true crabs which belong to Suborder Brachyura. True crabs have a hard, shortened abdomen which they fold under their hard shells for protection. Hermit crabs, on the other hand, have a soft, long abdomen. They have to insert this abdomen into an empty shell for protection. The soft abdomen is twisted to one side for a better fit into the spiral of a shell. There are appendages at the end of the abdomen to hang on tight to the shell. Hermits belong in their shells: Please don't try to pull hermit crabs out of their shells. You may rip out their little appendages or tear their delicate abdomens. Hermit parts: Unlike true crabs, hermit crabs have only two pairs of walking legs. They have long antennae and eyes on long stalks to peek out of the shell. Like true crabs, hermit crabs have two pincers. Both are used to feed with, and usually one is used to block the shell entrance when the hermit crabs retreats into its shell. This makes it more difficult for predators to pry them out of their shells. In some species, one of the pincers is much larger than the other. Hermit food: Some hermit crabs are scavengers. These have a keen sense of smell to find their food. Others eat algae and detritus. House hunting: As a hermit crab grows bigger, it has to find a bigger shell. A shell that is too small provides less effective protection from predators. Hermit crabs understood the concept of 'upgrading' long before other Singaporeans! Before switching shells, a hermit crab will tentativley test out the new shell first, while holding on to the old one. If the new one is not ideal, it instantly goes back into the old shell. A hermit crab does not necessarily always use the same kind of shell. Hermit crabs never kill the original occupant of the shell. They may, however, quarrel with each other over a desirable shell. Every shell on Chek Jawa is a potential hermit crab home. Even a tiny broken shell or an ugly shell covered with barnacles. One of the factors limiting the population of hermit crabs is the availability of suitable empty shells. So please don't take any shells away from Chek Jawa. Hermit babies: Hermit crabs have separate genders. To mate, hermits crabs partially emerge from their shells, releasing eggs and sperm simultaneously. The eggs hatch into free-swimming larvae that drift with the plankton before eventually settling down and developing into tiny hermit crabs. Some hermit crab females may brood their eggs inside their shells. Here is a fascinating photo of a hermit crab larva on Image Quest 3-D Marine Library Role in the ecosystem: Hermit crabs are eaten by many animals higher up in the food chain. Bigger crabs and birds can pry them out of their shells to eat them. Status and threats: The Land hermit crab is listed among the threatened animals of Singapore due to loss of our natural beaches.		Tiny hermit crabs in Button shells Striped hermit crab in a Moon snail shell Tidal hermit crab in a Spiral melongena snail shell Land hermit crab sealing its shell with its pincer

quick facts
1-6cm, in various kinds of shells, common

Classification:
Order Decapoda
Class Malacostraca
Subphylum Crustacea
Phylum Arthropoda

See also ...
Hermit crabs of Chek Jawa

Links
The Animated Hermit Crab on the OceanLink website: a marvellous animation of a hermit crab going in and out of its shell, with a fact sheet on hermit crabs.
Hermit crabs and their allies on the Marine Crustaceans of Southern Australia page on the Museum Victoria website: an introduction including a section on their biology which has lots of labelled diagrams, and photos and fact sheets on some hermits of Southern Australia.
Tidepool hermit crabs on the Waikiki Aquarium website: fact sheet with diagram.

Other references

Barnes, Robert D. & Ruppert, Edward E., 1996. Invertebrate Zoology. Harcourt College Publishers. 6th Edition. pp. 1056, G-1-16, I-1-30.
Pechenik, Jan A., 2000. Biology of the Invertebrates. McGraw-Hill Book Co., Singapore. 578 pp.
Ng, Peter K. L. & N. Sivasothi, 1999. A Guide to the Mangroves of Singapore II (Animal Diversity). Singapore Science Centre. 168 pp. online version
Tan, Leo W. H. & Ng, Peter K. L., 1988. A Guide to Seashore Life. The Singapore Science Centre, Singapore. 160 pp. online version
Davey, Keith, 1998. A Photographic Guide to Seashore Life of Australia. New Holland, Australia.144 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.
Chuang, S. H., 1961. On Malayan Shores. Muwu Shosa, Singapore. 225 pp., plates 1-112.

a companion website to the chek jawa guidebook website©ria tan 2003 www.wildsingapore.com

a companion website to the chek jawa guidebook
website©ria tan 2003 www.wildsingapore.com