Porcelain crabs Temporal range: | |
---|---|
Southeastern Pacific species of Petrolisthes, Allopetrolisthes and Liopetrolisthes | |
Scientific classification | |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Subphylum: | Crustacea |
Class: | Malacostraca |
Order: | Decapoda |
Infraorder: | Anomura |
Superfamily: | Galatheoidea |
Family: | Porcellanidae Haworth, 1825 |
Genera | |
See text |
Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. 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 age of the Late Jurassic epoch, 145–152 million years ago.
Porcelain crabs are small, usually with body widths less than 15 millimetres (9⁄16 inch). [1] They share the general body plan of a squat lobster, but their bodies are more compact and flattened, an adaptation for living and hiding under rocks. [2] Porcelain crabs are quite fragile animals, and often shed their limbs to escape predators, [3] hence their name. The lost appendage can grow back over several moults. Porcelain crabs have large chelae (claws), which are used for territorial struggles, but not for catching food. [1] The fifth pair of pereiopods is reduced and used for cleaning. [4]
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. [5] [6] 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), and the long antennae originating on the front outside of the eyestalks. [3] The abdomen of the porcelain crab is long and folded underneath it, free to move. [3]
Porcelain crabs live in all the world's oceans, except the Arctic Ocean and the Antarctic. [7] They are common under rocks, and can often be found and observed on rocky beaches and shorelines, startled creatures scurrying away when a stone is lifted. They feed by combing plankton and other organic particles from the water using long setae (feathery hair- or bristle-like structures) on the mouthparts. [4]
Some of the common species of porcelain crabs in the Caribbean Sea 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, Petrolisthes japonicus is common. [2]
As of 2018 [update] , some 4723 extant species of porcelain crab had been described, [8] [ citation needed ] divided among these 30 genera: [8] [9]
The fossil record of porcelain crabs includes species of Pachycheles, Pisidia, Polyonyx, Porcellana, and a further six genera known only from fossils: [10]
The earliest claimed porcelain crab fossil was Jurellana from the Tithonian aged Ernstbrunn Limestone of Austria. [10] However, it was subsequently determined to be a true crab. With the new oldest porcelain crab being Vibrissalana from the same locality. [11]
The Decapoda or decapods are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. Most decapods are scavengers. The order is estimated to contain nearly 15,000 species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with the shrimp and Anomura including hermit crabs, porcelain crabs, squat lobsters making up the bulk of the remainder. The earliest fossil decapod is the Devonian Palaeopalaemon.
Pleocyemata is a suborder of decapod crustaceans, erected by Martin Burkenroad in 1963. Burkenroad's classification replaced the earlier sub-orders of Natantia and Reptantia with the monophyletic groups Dendrobranchiata (prawns) and Pleocyemata. Pleocyemata contains all the members of the Reptantia, as well as the Stenopodidea, and Caridea, which contains the true shrimp.
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, alongside groups including the hermit crabs and mole crabs. They are distributed worldwide in the oceans, and occur from near the surface to deep sea hydrothermal vents, with one species occupying caves above sea level. More than 900 species have been described, in around 60 genera. Some species form dense aggregations, either on the sea floor or in the water column, and a small number are commercially fished.
Anomura is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans include the word crab, all true crabs are in the sister group to the Anomura, the Brachyura.
Carcinisation 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 described it as "one of the many attempts of Nature to evolve a crab". Most carcinised crustaceans belong to the infraorder Anomura.
Petrolisthes is a genus of marine porcelain crabs, containing these extant species:
Petrolisthes elongatus, known as the New Zealand half crab, elongated porcelain crab, blue half crab, blue false crab or simply as the half crab or false crab, is a species of porcelain crab native to New Zealand.
Neopetrolisthes maculatus is a species of porcelain crab from the Indo-Pacific region. It is a small, colourful crustacean with a porcelain-like shell. This porcelain crab is usually found within the stinging tentacles of a number of sea anemone species.
The Galatheidae are a family of squat lobsters.
Hippoidea is a superfamily of decapod crustaceans known as sand crabs, mole crabs.
Galathea is one of the largest genera of squat lobsters, containing 70 currently recognised species. Most species of Galathea live in shallow waters.
Enriquea leviantennata is a species of squat lobster in a monotypic genus in the family Munididae.
The Galatheoidea are a superfamily of decapod crustaceans comprising the porcelain crabs and some squat lobsters. Squat lobsters within the three families of the superfamily Chirostyloidea are not closely related to the squat lobsters within the Galatheoidea. The fossil record of the superfamily extends back to the Middle Jurassic genus Palaeomunidopsis.
Porcellana is a genus of decapod crustaceans in the widespread family Porcellanidae, the porcelain crabs, which superficially resemble true crabs. The genus Porcellana includes the following species:
Jurellana tithonia, the only species in the genus Jurellana, is a fossil crab. It was found in limestone rocks from the Ernstbrunn Formation in Austria, which have been dated to the Tithonian. It was originally thought to be the world's oldest porcelain crab, but was later determined to actually be a true crab.
Allopetrolisthes spinifrons is a species of porcelain crab. It displays "hypercarcinisation", whereby the resemblance to a true crab is enhanced by sexual dimorphism of the abdomen. It lives along the Pacific coast of Peru and Chile, as a symbiont of a sea anemone.
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.
The Munididae are a family of squat lobsters, taxonomically separated from the family Galatheidae in 2010.
Petrolisthes armatus, the green porcelain crab, is a species of small porcelain crab in the family Porcellanidae. It is believed to be native to Brazil but has spread to other parts of the world. Populations in the south eastern part of the United States have increased dramatically and the species is considered to be an invasive species.
Pachycheles is a genus of porcelain crabs in the family Porcellanidae. There are more than 40 described species in Pachycheles.