Porcelain crabs are decapod

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s in the widespread family Porcellanidae, which superficially resemble true

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

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 of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by the K ...

age of the

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

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, alongsi ...

, 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. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...

can grow back over several moults. Porcelain crabs have large

chelae A chela ()also called a claw, nipper, or pinceris a pincer (biology), pincer-like organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through New Latin '. The plural form is chelae. Legs bearing a chela are ...

(claws), which are used for

territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...

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 Carcinisation (or carcinization) is an example of convergent evolution in which a crustacean evolves into a crab-like form from a non-crab-like form. The term was introduced into evolutionary biology by L. A. Borradaile, who describe ...

, whereby a noncrab-like animal (in this case a relative of a squat lobster) evolves into an animal that resembles a

true crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

. 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 Dorsum (biology), 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 tor ...

), and the long antennae originating on the front outside of the

eyestalk In anatomy, an eyestalk (sometimes spelled eye stalk and also known as an ommatophore) is a protrusion that extends an eye away from the body, giving the eye a better field of view. It is a common feature in nature and frequently appears in fic ...

s. The

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

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 major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, a ...

and the

Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...

. 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, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc shel ...

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

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

and other organic particles from the water using long

seta In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. Th ...

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 ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

are ''

Petrolisthes quadratus ''Petrolisthes'' is a genus of marine porcelain crabs, containing these extant species: *'' Petrolisthes aegyptiacus'' Werding & Hiller, 2007 *'' Petrolisthes agassizii'' Faxon, 1893 *'' Petrolisthes amoenus'' (Guérin-Méneville, 1855) *'' Pe ...

'', found in large numbers under rocks in the intertidal, and the red-and-white polka-dotted ''

Porcellana sayana ''Porcellana sayana'' is a species of porcelain crab that lives in the western Atlantic Ocean, often as a commensal of hermit crabs. It is red with white spots, and has a characteristic bulge behind each claw. Distribution ''Porcellana sayana'' ...

'', which lives commensally within the shells inhabited by large

hermit crab Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit crab, most of which possess an a ...

s. In

Hong Kong Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China ( abbr. Hong Kong SAR or HKSAR), is a city and special administrative region of China on the eastern Pearl River Delt ...

, '' 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 ''Petrolisthes'' is a genus of marine porcelain crabs, containing these extant species: *'' Petrolisthes aegyptiacus'' Werding & Hiller, 2007 *'' Petrolisthes agassizii'' Faxon, 1893 *''Petrolisthes amoenus'' (Guérin-Méneville, 1855) *'' Pet ...

'' Stimpson, 1858 *''

Pisidia Pisidia (; grc-gre, Πισιδία, ; tr, Pisidya) 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 An ...

'' Leach, 1820 *'' Polyonyx'' Stimpson, 1858 *''

Porcellana ''Porcellana'' is a genus of Decapoda, decapod crustaceans in the widespread family (biology), family Porcellanidae, the porcelain crabs, which superficially resemble true crabs. The genus ''Porcellana'' includes the following species: * ''Por ...

'' 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 in ...

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 Ernstbrunn is a town in the district of Korneuburg in Lower Austria in Austria. Ernstbrunn takes up about 80.69 square kilometers, 26.99 percent of which is forest. The castle became the seat of the Ernstbrunn branch of the Counts of Sinzendorf ...

Limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

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

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