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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Anomurans
Porcelain crabs
Family Porcellanidae
updated Nov 13
if you learn only 3 things about them ...
They are NOT true crabs. Some differences from true crabs: only 3 pairs of walking legs, long antennae.
They drop their pincers when stressed, so don't harass them
Some live with other animals: sea pens, hermit crabs.

Where seen? Porcelain crabs are plentiful under the stones of our rocky shores, scattering in all directions as a stone is lifted. Some porcelain crabs live on or with other larger animals.

What are porcelain crabs? Porcelain crabs belong to the subgroup Anomura of the Order Decapoda. Anomurans includes hermit crabs. Porcelain crabs belong to Family Porcellanidae.

Features:
Body width 1cm or less. Body and pincers really flat, giving them a cartoonish appearance. But this form allows them to squeeze into nooks and crannies, and shelter in narrow places like under a stone.

Show of Arms: The porcelain crab's huge pincers are not used to catch prey. Porcelain crabs mostly filter feed peacefully using their feathery mouthparts (see below). Some species may use their pincers to snip off or scrape bits of algae, and others may scavenge on dead animals. Some species use their pincers mainly against rival porcelain crabs in territorial and other disputes.

Falling apart at the seams: The porcelain crab tends to shed limbs if stressed, hence its common name. This is a useful trait, in case a limb is trapped between rocks shifting in the currents, or grabbed by a predator. A dropped pincer may continue to move, to distract the predator while the owner makes its getaway. The lost limb eventually re-grows with subsequent moults, but this takes time.

Not a true crab! The porcelain crab is not a true crab. True crabs belong to the subgroup Brachyura and have four pairs of walking legs and short antennae. In comparison, porcelain crabs have only three pairs of walking legs and often have long antennae that emerge from outside the eyes, instead of between the eyes. The fourth pair of legs of the porcelain crab are short and folded along the sides of the body. The abdomen of the porcelain crab is long and folded under the body. The abdomen remains free to move. In fact, when alarmed, a submerged porcelain crab may swim upside down by flapping its abdomen!

What do they eat? Porcelain crabs filter feed at high tide. They have large mouthparts which are feathery with long silky hairs. These are extended into the water like nets to strain plankton from the water. Internal mouthparts scrape off any edible titbits caught on the hairs and transfer them to the mouth.

Porcelain babies: Porcelain crab eggs hatch into free-swimming larvae that only later settle down and develop into miniatures of their parents.

Role in the habitat: Some porcelain crabs live with other animals. One kind of porcelain crab lives on a sea pen. Elsewhere, there are porcelain crabs that live in a shell occupied by a hermit crab, with tubeworms, in the siphons of bivalves, among the tentacles of sea anemones, on or inside sponges, or up the backside of a sea cucumber!

Status and threats: Some of our porcelain crabs 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 also have an impact on local populations.

Huge flat pincers.

Long antennae emerging from outside
instead of between the eyes.

Changi, Jun 08


Feathery mouthparts.


Lazarus, Aug 12


Last pair of legs folded on
the sides of the body.
Changi, Jun 05

Porcelain crabs on Singapore shores



Family Porcellanidae recorded for Singapore
from Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
+from our observation
in red are those listed among the threatened animals of Singapore from Ng, P. K. L. & Y. C. Wee, 1994. The Singapore Red Data Book: Threatened Plants and Animals of Singapore.
*from WORMS

  Porcelain crabs seen awaiting identification
Species are difficult to positively identify without close examination.
On this website, they are grouped by external features for convenience of display.
  Hermit porcelain crab
Tiny brown porcelain crab
Commensal porcelain crabs

  Family Porcellanidae
  Eulanaios cometes (EN: Endangered)

Pachycheles sculptus

Petrolisthes sp. (Big porcelain crab) with species recorded in Singapore

Polyonyx biunguiculatus
Polyonyx obesulus
Polyonyx suluensis=**Aliaporcellana suluensis
Polyonyx telestophilus
Polyonyx triunguiculatus

Porcellana gordoni
Porcellana latifrons=*Lissoporcellana spinuligera
Porcellana quadrilobata=*Lissoporcellana quadrilobata
Porcellana streptochiroides
Porcellana corallicola=*Enosteoides ornatus

Porcellanella picta=*Porcellanella triloba
(Painted porcelain crab) (VU: Vulnerable)

Pseudoporcellanella manoliensis
(False porcelain crab) (VU: Vulnerable)

Raphidopus ciliatus
(VU: Vulnerable)
Raphidopus johnsoni

Links References
  • Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore. National Council on the Environment. 163pp.
  • Edward E. Ruppert, Richard S. Fox, Robert D. Barnes. 2004.Invertebrate Zoology Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963.
  • Pechenik, Jan A., 2005. Biology of the Invertebrates. 5th edition. McGraw-Hill Book Co., Singapore. 578 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.
  • Jones Diana S. and Gary J. Morgan, 2002. A Field Guide to Crustaceans of Australian Waters. Reed New Holland. 224 pp.
  • Debelius, Helmut, 2001. Crustacea Guide of the World: Atlantic Ocean, Indian Ocean, Pacific Ocean IKAN-Unterwasserachiv, Frankfurt. 321 pp.
  • Gosliner, Terrence M., David W. Behrens and Gary C. Williams. 1996. Coral Reef Animals of the Indo-Pacific: Animal life from Africa to Hawaii exclusive of the vertebrates Sea Challengers. 314pp.
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