Porcelain crabs are

decapod The Decapoda or decapods, from Ancient Greek δεκάς (''dekás''), meaning "ten", and πούς (''poús''), meaning "foot", is a large order of crustaceans within the class Malacostraca, and includes crabs, lobsters, crayfish, shrimp, and p ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s in the widespread family Porcellanidae, which superficially resemble true

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

s. They have flattened bodies as an adaptation for living in rock crevices. They are delicate, readily losing limbs when attacked, and use their large claws for maintaining territories. They first appeared in the

Tithonian In the geological timescale, the Tithonian is the latest age (geology), age of the Late Jurassic Epoch and the uppermost stage (stratigraphy), stage of the Upper Jurassic Series. It spans the time between 149.2 ±0.7 annum, Ma and 143.1 ±0.6 (mi ...

age of the

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

epoch, 145–152 million years ago.

Description

Porcelain crabs are small, usually with body widths less than . They share the general body plan of a

squat lobster Squat lobsters are dorsoventrally flattened crustaceans with long tails held curled beneath the cephalothorax. They are found in the two superfamilies Galatheoidea and Chirostyloidea, which form part of the decapod infraorder Anomura, alongs ...

, but their bodies are more compact and flattened, an adaptation for living and hiding under rocks. Porcelain crabs are quite fragile animals, and often shed their limbs to escape predators, hence their name. The lost

appendage An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...

can grow back over several moults. Porcelain crabs have large chelae (claws), which are used for

territorial A territory is an area of land, sea, or space, belonging or connected to a particular country, person, or animal. In international politics, a territory is usually a geographic area which has not been granted the powers of self-government, ...

struggles, but not for catching food. The fifth pair of pereiopods is reduced and used for cleaning.

Evolution

Porcelain crabs are an example of carcinisation, whereby a noncrab-like animal (in this case a relative of a squat lobster) evolves into an animal that resembles a true crab. Porcelain crabs can be distinguished from true crabs by the apparent number of walking legs (three instead of four pairs; the fourth pair is reduced and held against the

carapace A carapace is a dorsal (upper) 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 turtles and tortoises. In turtles and tortoises, the unde ...

), and the long antennae originating on the front outside of the eyestalks. The

abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

of the porcelain crab is long and folded underneath it, free to move.

Biogeography and ecology

Porcelain crabs live in all the world's oceans, except the

Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five oceanic divisions. It spans an area of approximately and is the coldest of the world's oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, ...

and the

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

. They are common under rocks, and can often be found and observed on rocky

beach A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from Rock (geology), rock, such as sand, gravel, shingle beach, shingle, pebbles, etc., or biological s ...

es and shorelines, startled creatures scurrying away when a stone is lifted. They feed by combing

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

and other organic particles from the water using long

seta In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae, ...

e (feathery hair- or bristle-like structures) on the mouthparts. Some of the common species of porcelain crabs in the

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

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 crabs. In

Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...

, '' Petrolisthes japonicus'' is common.

Diversity

, some 4723 extant species of porcelain crab had been described, divided among these 30 genera: *'' Aliaporcellana'' Nakasone & Miyake, 1969 *'' Allopetrolisthes'' Haig, 1960 *'' Ancylocheles'' Haig, 1978 *'' Capilliporcellana'' Haig, 1978 *'' Clastotoechus'' Haig, 1960 *'' Enosteoides'' Johnson, 1970 *'' Euceramus'' Stimpson, 1860 *'' Eulenaios'' Ng & Nakasone, 1993 *'' Heteropolyonyx'' Osawa, 2001 *'' Heteroporcellana'' Haig, 1978 *'' Liopetrolisthes'' Haig, 1960 *'' Lissoporcellana'' Haig, 1978 *'' Madarateuchus'' Harvey, 1999 *'' Megalobrachium'' Stimpson, 1858 *'' Minyocerus'' Stimpson, 1858 *'' Neopetrolisthes'' Miyake, 1937 *'' Neopisosoma'' Haig, 1960 *'' Novorostrum'' Osawa, 1998 *'' Orthochela'' Glassell, 1936 *'' Pachycheles'' Stimpson, 1858 *'' Parapetrolisthes'' Haig, 1962 *'' Petrocheles'' Miers, 1876 *'' Petrolisthes'' Stimpson, 1858 *''

Pisidia Pisidia (; , ; ) was a region of ancient Asia Minor located north of Pamphylia, northeast of Lycia, west of Isauria and Cilicia, and south of Phrygia, corresponding roughly to the modern-day province of Antalya in Turkey. Among Pisidia's set ...

'' Leach, 1820 *'' Polyonyx'' Stimpson, 1858 *'' Porcellana'' Lamarck, 1801 *'' Porcellanella'' White, 1852 *'' Pseudoporcellanella'' Sankarankutty, 1962 *'' Raphidopus'' Stimpson, 1858 *'' Ulloaia'' Glassell, 1938 The

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

of porcelain crabs includes species of ''Pachycheles'', ''Pisidia'', ''Polyonyx'', ''Porcellana'', and a further six genera known only from fossils: *'' Annieporcellana'' Fraaije ''et al.'', 2008 *'' Beripetrolisthes'' De Angeli & Garassino, 2002 *'' Eopetrolisthes'' De Angeli & Garassino, 2002 *'' Lobipetrolisthes'' De Angeli & Garassino, 2002 *'' Longoporcellana'' Müller & Collins, 1991 The earliest claimed porcelain crab fossil was '' Jurellana'' from the

aged Ernstbrunn

Limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

of Austria. However, it was subsequently determined to be a true crab. With the new oldest porcelain crab being '' Vibrissalana'' from the same locality.

References

External links

* {{Taxonbar, from=Q1435521 Anomura Tithonian first appearances Extant Late Jurassic first appearances Taxa named by Adrian Hardy Haworth