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
live with other animals: sea pens, hermit crabs.
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.
antennae emerging from outside
instead of between the eyes.
pair of legs folded on
the sides of the body.
|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
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!
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.
crabs on Singapore shores
|Other sightings on Singapore shores
Kusu Island, Jul 20
Photo shared by Jianlin Liu on facebook.
Family Porcellanidae recorded for Singapore
Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity
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.
+Other additions (Singapore Biodiversity Records, etc)
++from The Biodiversity of Singapore, Lee Kong Chian Natural History Museum.
crabs seen awaiting identification
are difficult to positively identify without close examination.
On this website, they are grouped by external features for convenience
cometes (EN: Endangered)
(Big porcelain crab) with species recorded in Singapore
Polyonyx suluensis=^Aliaporcellana suluensis
Porcellana latifrons=^Lissoporcellana spinuligera
Porcellana quadrilobata=^Lissoporcellana quadrilobata
Porcellana corallicola=^Enosteoides ornatus
Porcellanella picta=^Porcellanella triloba
(Painted porcelain crab) (VU: Vulnerable)
(False porcelain crab) (VU: Vulnerable)
Raphidopus ciliatus (VU: Vulnerable)
Crab (Petrolisthes) Tan, Leo W. H. & Ng, Peter K. L.,
Guide to Seashore Life. The Singapore Science Centre,
Singapore. 160 pp.
porcelain crab (Petrolisthes kranjiensis) Ng, Peter
K. L. & N. Sivasothi, 1999. A
Guide to the Mangroves of Singapore II (Animal Diversity).
Singapore Science Centre. 168 pp.
- Krystal L.
Rypien and A. Richard Palmer, The
effects of sex, size and habitat on the incidence of puncture
wounds in the claws of the porcelain crab Petrolisthes cinctipes
(Anomura: Porcellanidae). Journal of Crustacean Biology 27(1):59-64.
2007 doi: http://dx.doi.org/10.1651/S-2728.1
- Roy K. Kropp.
Additional Porcelain Crab Feeding Methods (Decapoda, Porcellanidae)
Crustaceana Vol. 40, No. 3 (May, 1981), pp. 307-310.
- M. Osawa & P. K. L. Ng. 29 June 2016. Revision of Polyonyx pedalis Nobili, 1906 (Crustacea: Decapoda: Anomura: Porcellanidae), with descriptions of three new species. The Raffles Bulletin of Zoology 2016 Supplement No. 34 (Part I of II) Pp. 499-518.
- 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
Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963.
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.
Helmut, 2001. Crustacea
Guide of the World: Atlantic Ocean, Indian Ocean, Pacific Ocean
IKAN-Unterwasserachiv, Frankfurt. 321 pp.
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.