Emerita (crustacean)

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Emerita
Female Emerita analoga
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Anomura
Family: Hippidae
Genus: Emerita
Scopoli, 1777 [1]
Type species
Cancer emeritus
Linnaeus, 1767 [2]

Emerita is a small genus of decapod crustaceans,[3] known as sand crabs, or mole crabs. These small animals burrow in the sand in the swash zone and use their antennae for filter feeding.[4][5]

Description[edit]

Emerita has a barrel-shaped body. It has a tough exoskeleton and can hold its appendages close to the body, allowing it to roll in the tidal currents and waves.[6] It has feathery antennae, which are used to filter plankton and detritus from the swash.[6]

Males are typically smaller than females, and in some species, such as Emerita rathbunae, the minute males live attached to the legs of the female.[7] Females are around 8–37 mm (0.31–1.46 in) in carapace length, depending on the species, while males vary from a similar size to females in E. austroafricana, down to 2.5 mm (0.098 in) carapace length in E. rathbunae and E. talpoida.[8]

Distribution[edit]

The genus as a whole has a broad distribution in tropical and subtropical regions. Most individual species, however, are restricted to smaller areas, and their ranges rarely overlap.[9] The genus is common on both coasts of the United States and along the Atlantic coast of Africa; the related genus Hippa is found across the Indo-Pacific, including Australia.[10]

Species[edit]

Twelve species are recognised:[3][Note 1]

The Old World species had been widely thought to form a monophyletic group, as did the New World species. The use of molecular phylogenetics has shown, however, that E. analoga, a species living along the Pacific coast of North America, is more closely related to African species than it is to other New World species.[9]

Taxonomy[edit]

The genus Emerita was erected by Giovanni Antonio Scopoli in his 1777 work Introductio ad Historiam Naturalem.[11] The type species is Cancer emeritus (now E. emeritus), because at one time, it was the only species in the genus.[2] Other genera with the same name have been rejected for nomenclatural purposes; these were published by Laurens Theodorus Gronovius (1764) and Friedrich Christian Meuschen (1778 and 1781).[1]

Ecology and behaviour[edit]

E. analoga digging in the sand

Emerita is adept at burrowing, and is capable of burying itself completely in 1.5 seconds.[6] Unlike mud shrimp, Emerita burrows tail-first into the sand, using the pereiopods to scrape the sand from underneath its body.[12] During this action, the carapace is pressed into the sand as anchorage for the digging limbs.[12] The digging requires the sand to be fluidised by wave action, and Emerita must bury itself in the correct orientation before the wave has passed to be safe from predators.[12]

As the tide changes, Emerita changes its position on the beach;[6] most individuals stay in the zone of breaking waves.[7] This may be detected by the physical characteristics of the sand. As the tide falls, the sand is allowed to settle; when Emerita detects this, it uses the temporary liquefaction from a breaking wave to emerge from its burrow, and is carried down the beach by the wave action.[7] Longshore drift may also drag Emerita laterally along a beach.[7]

The main predators of Emerita are fish; in the eastern Pacific Ocean, the barred surfperch (Amphistichus argenteus) is particularly important.[7] Seabirds also eat Emerita, but do not appear to target the aggregations of mole crabs.[7] Carcasses of Emerita provide an important food source for the closely related scavenger Blepharipoda.[7]

Relationship to humans[edit]

Due to the Emerita being the predominant diet of the barred surfperch, surf fishermen use sand crabs as bait. Soft-shelled Emerita are kept also as bait by commercial fisheries.

In some cultures, sand crabs are eaten as a popular snack, such as in Thailand. They are often prepared via shallow frying in a pan or deep frying in batter. The taste is often described as falling somewhere between that of shrimp and crab. Eating sand crabs presents a risk of paralytic shellfish poisoning and/or infection with Profilicollis parasites.[13] In Malaysia, the sand crab locally known as yat yat, ibu remis, kutu laut or udang pasir can be found along the beaches in Kelantan during the monsoon season. The crab is a local delicacy that is usually fried with eggs or roasted on a skewer like satay.[14]

Life cycle[edit]

Eggs on the underside of a female E. analoga

Emerita has a short lifespan, perhaps no more than two to three years, and can reproduce in its first year of life.[7] The eggs are bright orange, and hatch into larvae, which may live as plankton for more than four months and can be carried long distances by ocean currents.[7] The number of zoeal stages varies between species from six to eleven.[2]

See also[edit]

Notes[edit]

  1. ^ Distributions follow Haye et al. (2003).[9]

References[edit]

  1. ^ a b International Commission on Zoological Nomenclature (1963). "Opinion 643. Idotea Fabricius, 1798, and Mesidotea Richardson, 1905 (Crustacea, Decapoda); validation under the Plenary Powers". Bulletin of Zoological Nomenclature. 20 (1): 18–25.
  2. ^ a b c Christopher B. Boyko; Patsy A. McLaughlin (2010). Martyn E. Y. Low; S. H. Tan (eds.). "Annotated checklist of anomuran decapod crustaceans of the world (exclusive of the Kiwaoidea and families Chirostylidae and Galatheidae of the Galatheoidea): Part IV – Hippoidea" (PDF). Zootaxa. Suppl. 23: 109–129. Archived from the original (PDF) on 2012-03-16.
  3. ^ a b DecaNet (2023). "Emerita Scopoli, 1777". WoRMS. World Register of Marine Species. Retrieved 1 June 2023.
  4. ^ Sand Fleas (Mole Crabs or Sand Crabs) Prime surf fishing bait
  5. ^ http://www.baymoon.com/~ilga/crabs/ All About Mole Crabs
  6. ^ a b c d Kenneth Henry Mann (2000). "Sandy beaches". Ecology of Coastal Waters, with Implications for Management. Volume 8 of Studies in Ecology (2nd ed.). Wiley-Blackwell. pp. 218–236. ISBN 978-0-86542-550-7.
  7. ^ a b c d e f g h i Edward F. Ricketts; Jack Calvin; David W. Phillips & Joel W. Hedgpeth (1992). "Open-coast sandy beaches". Between Pacific Tides (5th ed.). Stanford University Press. pp. 249–265. ISBN 978-0-8047-2068-7.
  8. ^ T. Subramoniam (1981). "Protandric hermaphroditism in a mole crab, Emerita asiatica (Decapoda:Anomura)". Biological Bulletin. 160 (1): 161–174. doi:10.2307/1540910. JSTOR 1540910. BIOSTOR 9638.
  9. ^ a b c Haye, Pilar A.; Yan K. Tam; Irv Kornfield (2002). "Molecular phylogenetics of mole crabs (Hippidae: Emerita)" (PDF). Journal of Crustacean Biology. 22 (4): 903–915. doi:10.1651/0278-0372(2002)022[0903:MPOMHE]2.0.CO;2. JSTOR 1549850. S2CID 7216390.
  10. ^ Colin Little (2000). "The coarse extreme: life on sandy beaches". The Biology of Soft Shores and Estuaries. Oxford University Press. pp. 35–57. ISBN 978-0-19-850426-9.
  11. ^ Ioannis Ant. Scopoli (1777). Introductio ad historiam naturalem sistens genera lapidum, plantarum, et animalium hactenus detecta, caracteribus essentialibus donata, in tribus divisa, subinde ad leges naturae (in Latin). Prague: Wolfgang Gerle.
  12. ^ a b c Adolf Seilacher (2007). "Plate 21. Burrowing techniques". Trace Fossil Analysis. Springer. p. 64. ISBN 978-3-540-47225-4.
  13. ^ Lombard, Kirk (2016). The sea forager's guide to the Northern California coast. Leighton Kelly. Berkeley, California. ISBN 978-1-59714-357-8. OCLC 948549931.{{cite book}}: CS1 maint: location missing publisher (link)
  14. ^ Nor Amalina Alias (13 December 2020). "Seronok kutip Yat Yat [METROTV]". Harian Metro (in Malay). Retrieved 29 August 2021.

External links[edit]

  • Media related to Emerita at Wikimedia Commons