Porcelain crabs are
decapodThe decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers.-Anatomy:...
crustaceans in the family Porcellanidae, which superficially resemble true
crabCrabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax.Crabs have a soft body covered with a hard shell. They are generally covered with a thick exoskeleton, and armed with a...
s. They are a good example of
carcinisationIn evolutionary biology, carcinisation is a hypothesised process whereby a crustacean evolves into a crab-like form from a non-crab-like form. The term was introduced by L. A...
, whereby a non-crab-like animal (in this case a relative of a
squat lobsterSquat lobsters are decapod crustaceans of the families Galatheidae and Chirostylidae, including the common genera Galathea and Munida. They are not lobsters at all, but are more closely related to porcelain crabs, hermit crabs and then, more distantly, true crabs. They are distributed worldwide...
) evolves into an animal that only a specialist would know is not a true crab. They live in all the world's oceans, except the
Arctic OceanThe Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest, and shallowest of the world's five major oceanic divisions.
The International Hydrographic Organization recognizes it as an ocean, although some...
and the
AntarcticThe Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...
.
Porcelain crabs are small, usually with body widths of 1-2 cm.
They are common under rocks, and can often be found and observed on rocky
beachA beach is a geological landform along the shoreline of a body of water. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles, or cobblestones...
es and shorelines, startled creatures scurrying away when a stone is lifted.
Porcelain crabs can be distinguished from the true crabs by the apparent number of walking legs (three instead of four pairs, the fourth pair is actually hidden under the
carapaceA carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids as well as vertebrates such as chelonians, order Testudines, turtles and tortoises.-Crustaceans:In crustaceans, the carapace is a part of the exoskeleton...
), the apparent lack of a wrist (carpal) segment on the chelipeds, and long
antennaeAntennae in biology have historically been paired appendages used for sensing in arthropods and crustaceans. More recently, the term has also been applied to cilium structures present in many cell types of eukaryotes....
originating on the front outside of the eye stalks. The
abdomenIn vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
of the porcelain crab is long and folded underneath it, free to move. In fact, when alarmed, the crab might swim by flapping its abdomen.
Porcelain crabs share the general body plan of a
squat lobsterSquat lobsters are decapod crustaceans of the families Galatheidae and Chirostylidae, including the common genera Galathea and Munida. They are not lobsters at all, but are more closely related to porcelain crabs, hermit crabs and then, more distantly, true crabs. They are distributed worldwide...
(Galatheidae), but their bodies are more compact and flattened, an adaptation for living and hiding under rocks, as well as squeezing into little nooks and crannies. The porcelain crabs are quite fragile animals, and will often shed their limbs, hence their name. This trait is useful for these crustaceans because it helps them escape if a limb is grabbed by a predator or caught between rocks shifting in the current. A broken-off piece of limb may still continue to move for a short while, distracting the would-be predator as the crustacean flees. The lost
appendageAn appendage in the broadest sense is an additional or subsidiary part existing on, or added to, something which can generally still function if the appendage has never existed or is later provided or grown, or will still perform a primary function if the appendage is removed.- Biological context...
can grow back over several
moultingsEcdysis is the moulting of the cuticula in arthropods and related groups . Since the cuticula of these animals is also the skeletal support of the body and is inelastic, it is shed during growth and a new, larger covering is formed...
. Porcelain crabs have large
chelae (
clawA claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end...
s), which are used for
territorialIn ethology, sociobiology and behavioral ecology, the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics...
struggles, but not for catching food.
Feeding is accomplished instead by combing
planktonPlankton consist of any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than their phylogenetic or taxonomic classification...
and other organic particles from the water using long
setaSeta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....
e (feathery hair or bristle-like structures) on the mouthparts, where they will later be scraped off and consumed into the mouth. These animals will also scavenge on the sea floor for
detritusDetritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
and in
aquariaAn aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
, they will consume meaty pieces of
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
or
shrimpShrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
.
Some of the common species of porcellanids in the
CaribbeanThe Caribbean Sea is a sea of the Atlantic Ocean situated in the tropics of the Western hemisphere, bounded to the south and west by the American landmass, with the North Atlantic Ocean proper to the northeast and the Gulf of Mexico to the northwest...
are
Petrolisthes quadratus, found in large numbers under rocks in the intertidal, and the red-and-white polka-dotted
Porcellana sayana, which lives commensally within the shells inhabited by large
hermit crabHermit crabs are decapod crustaceans of the superfamily Paguroidea. They are not closely related to true crabs. Hermit crabs are quite commonly seen in the intertidal zone: for example, in tide pools....
s.
Genera
- Aliaporcellana Nakasone & Miyake, 1969
- Capilliporcellana Haig, 1981
- Clastotoechus Haig, 1960
- Euceramus Stimpson, 1858
- Enosteoides Johnson, 1970
- Eulenaios Ng & Nakasone, 1993
- Lissoporcellana Haig, 1978
- Megalobrachuium Stimpson, 1858
- Minyocerus Stimpson, 1858
- Neopetrolisthes Miyake, 1937
- Neopisoma Haig, 1960
- Pachycheles Ward, 1942
- Parapetrolisthes Haig, 1962
- Petrolisthes
Petrolisthes is a genus of marine porcelain crabs.-Species:* Petrolisthes aegyptiacus
Werding & Hiller, 2007* Petrolisthes amoenus
...
StimpsonWilliam Stimpson was a noted American scientist.Stimpson was born in Boston, Massachusetts and studied under the great naturalist Louis Agassiz....
, 1858
- Pisidia Leach, 1820
- Polyonyx Stimpson, 1858
- Porcellana Lamarck, 1801
- Porcellanella White, 1852
- Pseudoporcellanella Sankarankutty, 1961
- Raphidopus Stimpson, 1858
- Ulloaia Glassell, 1938