Pebble crabs (phylum Arthropoda, subphylum Crustacea, class Malacostraca, order Decapoda, superfamily Leucosioidea, family Leucosiidae) usually have circular, oval or pentagonal carapaces. Many species have a convex carapace, and appear much like round pebbles, and hence the common name.
The eyes and antennae are very tiny and hardly noticeable, and the chelipeds are symmetrical. Most pebble crabs are adapted for burrowing, and are found in soft substrates like sand or mud. Many species feed on tiny invertebrates by probing the top layer of the sediment and capturing the ones disturbed.
Like other crabs, pebble crabs have a broad carapace, and a very short and flattened abdomen which is usually folded underneath the body. They also have five pairs of "legs" (including the clawed arms, or chelipeds), and hence they are placed in the order Decapoda ("deca" means "ten", while "poda" means "feet"). The gills are leaf-like - a distinctive characteristic of decapods from the suborder Pleocyemata. And as with other crustaceans from the class Malacostraca, their body comprises three main parts - a head with five segments, a thorax with eight segments, and an abdomen with six segments. The head is fused to the thorax, forming a cephalothorax. They have a tough exoskeleton strengthened with calcium carbonate, and the carapace covers the gills but not the abdomen.
Pebble crabs reproduce sexually, and have separate sexes. They mate face-to-face, usually with the male on top and the female below. The females can usually be distinguished from the males by having a broader abdomen. This is an adaptation to allow them to carry the eggs under their abdomen until they hatch.
Unfortunately, I am still unable to identify the species of pebble crabs that I have seen so far.
References
The eyes and antennae are very tiny and hardly noticeable, and the chelipeds are symmetrical. Most pebble crabs are adapted for burrowing, and are found in soft substrates like sand or mud. Many species feed on tiny invertebrates by probing the top layer of the sediment and capturing the ones disturbed.
Like other crabs, pebble crabs have a broad carapace, and a very short and flattened abdomen which is usually folded underneath the body. They also have five pairs of "legs" (including the clawed arms, or chelipeds), and hence they are placed in the order Decapoda ("deca" means "ten", while "poda" means "feet"). The gills are leaf-like - a distinctive characteristic of decapods from the suborder Pleocyemata. And as with other crustaceans from the class Malacostraca, their body comprises three main parts - a head with five segments, a thorax with eight segments, and an abdomen with six segments. The head is fused to the thorax, forming a cephalothorax. They have a tough exoskeleton strengthened with calcium carbonate, and the carapace covers the gills but not the abdomen.
Pebble crabs reproduce sexually, and have separate sexes. They mate face-to-face, usually with the male on top and the female below. The females can usually be distinguished from the males by having a broader abdomen. This is an adaptation to allow them to carry the eggs under their abdomen until they hatch.
Unfortunately, I am still unable to identify the species of pebble crabs that I have seen so far.
References
- De Grave, S., N. D. Pentcheff , S. T. Ahyong, T.-Y. Chan, K. A. Crandall, P. C. Dworschak, D. L. Felder, R. M. Feldmann, C. H. J. M. Fransen, L. Y. D. Goulding, R. Lemaitre, M. E. Y. Low, J. W. Martin, P. K. L. Ng, C. E. Schweitzer, S. H. Tan, D. Tshudy & R. Wetzer. 2009. A classification of living and fossil genera of decapod crustaceans. The Raffles Bulletin of Zoology, supplement 21, pp. 1-109.
- Debelius, H. 1999. Crustacea - Guide of the world. IKAN, Frankfurt. 321pp.
- Ng, P. K. L., S. S. L. Lim, L. K. Wang & L. W. H. Tan. 2007. Private lives: An exposé of Singapore's shores. Raffles Museum of Biodiversity Research, Department of Biological Sciences, National University of Singapore. 212 pp.
- Ng, P. K .L., R. T. Corlett & H.T.W. Tan (eds.). 2011. Singapore biodiversity: An encyclopedia of the natural environment and sustainable development. Singapore: Editions Didier Millet. 552 pp.
- World Register of Marine Species. 2012. Retrieved Jun 10, 2013, from http://www.marinespecies.org.
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