Porcelain crab explained

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.

Description

Porcelain crabs are small, usually with body widths less than 15frac=-16NaNfrac=-16.[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. Porcelain crabs are quite fragile animals, and often shed their limbs to escape predators, 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.[2]

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.[3] [4] 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.[5] The abdomen of the porcelain crab is long and folded underneath it, free to move.[5]

Biogeography and ecology

Porcelain crabs live in all the world's oceans, except the Arctic Ocean and the Antarctic.[6] 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.[2]

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.[7]

Diversity

, some 4723 extant species of porcelain crab had been described,[8] 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]

Notes and References

  1. Book: Mark W. . Denny . Steven Dean . Gaines . amp . 2007 . Encyclopedia of Tidepools and Rocky Shores . Encyclopedias of the Natural World, Issue 1 . . 978-0-520-25118-2 . Crabs . 164–176 . https://books.google.com/books?id=uufQnE7MzMkC&pg=PA167.
  2. Book: Allen, Gerald R. . 1997 . Tropical Marine Life . Periplus Nature Guides . . 978-962-593-157-9 . Anemone crab Neopetrolisthes maculatus . 35 . https://books.google.com/books?id=vpMSjJ5DVDYC&pg=PA35.
  3. C. L. Morrison . A. W. Harvey . S. Lavery . K. Tieu . Y. Huang . C. W. Cunningham . 2001 . Mitochondrial gene rearrangements confirm the parallel evolution of the crab-like form . . 269 . 345–350 . 10.1098/rspb.2001.1886 . 1489 . 11886621 . 1690904.
  4. Jonas Keiler, Stefan Richter . Christian S. Wirkner . amp . 2014 . Evolutionary morphology of the organ systems in squat lobsters and porcelain crabs (crustacea: Decapoda: Anomala): an insight into carcinization . . 10.1002/jmor.20311 . 25156549 . 276 . 1 . 1–21. 26260996 .
  5. Book: Gary C. B. Poore . Shane T. Ahyong . amp . 2004 . Marine decapod Crustacea of southern Australia: a guide to identification . . 978-0-643-06906-0 . Porcellanidae Haworth, 1825 . 242–246 . https://books.google.com/books?id=ZZWnuGc0xlMC&pg=PA242.
  6. Web site: Porcellanidae Haworth, 1825 . P. McLaughlin, S. Ahyong . J. K. Lowry . amp . October 2, 2002 . Anomura: Families . . February 10, 2005 . https://web.archive.org/web/20050429024213/http://crustacea.net/crustace/anomura/www/porcella.htm . April 29, 2005 . dead .
  7. Book: Brian Morton . John Edward Morton . amp . 1993 . The Sea Shore Ecology of Hong Kong . . 978-962-209-027-9 . Boulder shores . 86–125 . https://books.google.com/books?id=r79kKRbkzMwC&pg=PA95.
  8. Masayuki Osawa . Patsy A. McLaughlin . amp . 2010 . Annotated checklist of anomuran decapod crustaceans of the world (exclusive of the Kiwaoidea and families Chirostylidae and Galatheidae of the Galatheoidea) Part II – Porcellanidae . . Suppl. 23 . 109–129 . dead . https://web.archive.org/web/20120302185947/http://rmbr.nus.edu.sg/rbz/biblio/s23/s23rbz109-129.pdf . 2012-03-02 .
  9. Web site: WoRMS . 2010 . Porcellanidae . . November 13, 2010.
  10. Carrie E. Schweitzer . Rodney M. Feldmann . amp . 2010 . Earliest known Porcellanidae (Decapoda: Anomura: Galatheoidea) (Jurassic: Tithonian) . . 258 . 2 . 243–248 . 10.1127/0077-7749/2010/0096.
  11. Robins. Cristina M. Klompmaker. Adiël A. 2019-11-14. Extreme diversity and parasitism of Late Jurassic squat lobsters (Decapoda: Galatheoidea) and the oldest records of porcellanids and galatheids. Zoological Journal of the Linnean Society. en. 187. 4. 1131–1154. 10.1093/zoolinnean/zlz067. 0024-4082. free.

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