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Encope emarginata

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Encope emarginata, a notched sand dollar, is a marine echinoid ranging the western Atlantic ocean. They are best known for their bioturbation in the sediment, relationship with crabs, and their widespread distribution.

Encope emarginata
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Echinodermata
Class: Echinoidea
Order: Clypeasteroida
Family: Mellitidae
Genus: Encope
Species:
E. emarginata
Binomial name
Encope emarginata
(Leske, 1778)

Description

E. emarginata has a thick test, or shell, that often remains intact and preserved.[1] Tests are oval-shaped, centrally domed, typically greenish-brown colored, and have 6 lunules, or notches, as well as large bowed petaloids [2] Young E. emarginata can be mistaken for its sibling, E. michelini, because of the presence of open lunules as juveniles, although closed as adults.[3]

Basic anatomy of E. emarginata

Habitat and Distribution

Notched Sand Dollar found on coast of Brazil by @fernandas via iNaturalist

Mostly found in subtropical and tropical waters of the Caribbean Sea, Gulf of Mexico, and southwestern Atlantic Ocean, E. emarginata ranges from Belize to Argentina.[4] Common on the South America Atlantic coastline, they are one of the only extant echinoids found on the coast of Rio Grande do Sul (the other being Mellita quinquiesperforata) and the only one south of the La Plata river.[5] Area inhibited by Encope emarginata is below the action of the normal wave regime, thus the fossils of this species is only truly disturbed during extreme coastal weather.[5]

E. emarginata inhabits sandy, muddy sediments of coastal waters.[4] Although a marine species,[6] they have also been found in estuaries and river mouths.[7] The waters they live in are typically shallow, as deep as 20 meters.[8]

Taxonomy

These sand dollars were originally named Echinodiscus emarginatus,[9] but have since been transferred to the Encope genus within the Mellitidae family.[6] Encope is thought to be the most diverse genus among sand dollars, containing 7 extant species.[1] Fossils can be dated back to the Pliocene or Pleistocene, up to 5 million years ago.[1]

There is ongoing research suggesting that two populations of E. emarginata may emerge as separate species as a result of a barrier created by upwelling, a process known as allopatric speciation.[4]

Bioturbation

E. emarginata is well-known for its bioturbation within the sediment, especially its effect on the spatial distributions of phytoplankton and other small benthic organisms. Moving at a maximum rate of 15 cm per hour, these sand dollars typically work through surface-layer sediments. E. emarginata has shown to have significant impacts on the concentrations of Chlorophyll-a within the sediment, as well as causing a greater variance in microphytobethic and meiofaunal populations due to the sand dollars' foraging behaviors. The bioturbation of this echinoid is thought to create top-down effects, enhancing sediment heterogeneity and maintaining benthic biodiversity.[10]

E. emarginata in the Natural History Museum in London, England

Relationship with Ectosymbiotic Crabs

Genus Dissodactylus are commensal or parasitic crabs found to live on the bodies of irregular echinoids, such as E. emarginata. There is ongoing debate whether the size of E.emarginata influences the number of crabs found on it, where one study found a positive correlation[11] and another found no relationship.[12] The crabs are thought to consume the spines of the sand dollar, but additional research is necessary to determine if the Dissodactylus are truly parasitic.[11]

References

  1. ^ a b c Coppard, Simon E.; Lessios, H. A. (2017-09-14). "Phylogeography of the sand dollar genus Encope: implications regarding the Central American Isthmus and rates of molecular evolution". Scientific Reports. 7 (1): 11520. doi:10.1038/s41598-017-11875-w. ISSN 2045-2322. PMC 5599539. PMID 28912431.
  2. ^ "Encope emarginata - Plazi TreatmentBank". treatment.plazi.org. Retrieved 2023-03-23.
  3. ^ Francisco, V.; Pauls, S. M. (2008). "Especies del Orden Clypeasteroida (Echinodermata: Echinoidea) de las costas de Venezuela". Revista de Biología Tropical. 56 (3): 215–228. ISSN 0034-7744.
  4. ^ a b c Ventura, C; Hopkins, T; Kuhajda, B (2004-12-15), "Morphological dimensional differences in two geographically separated populations of Encope emarginata (Leske) from the coast of Brazil", Echinoderms: Munchen, Taylor & Francis, pp. 261–265, doi:10.1201/9780203970881.ch45, ISBN 978-0-415-36481-2, retrieved 2023-02-20
  5. ^ a b Lopes, Renato Pereira (2011-12-30). "Fossil sand dollars (Echinoidea: Clypeasteroida) from the Southern Brazilian coast". Revista Brasileira de Paleontologia. 14 (3): 201–214. doi:10.4072/rbp.2011.3.01. ISSN 1519-7530.
  6. ^ a b "WoRMS - World Register of Marine Species - Encope emarginata (Leske, 1778)". www.marinespecies.org. Retrieved 2023-02-20.
  7. ^ Brustolin, Marco C.; Thomas, Micheli C.; Mafra, Luiz L.; da Cunha Lana, Paulo (2016-05-20). "Bioturbation by the sand dollar Encope emarginata (Echinoidea, Mellitidae) changes the composition and size structure of microphytobenthic assemblages". Hydrobiologia. 779 (1): 183–192. doi:10.1007/s10750-016-2815-6. ISSN 0018-8158. S2CID 254554493.
  8. ^ Biología Tropical, Revista de (2015-06-01). "Indice y Creditos". Revista de Biología Tropical. 63 (2): 1. doi:10.15517/rbt.v63i2.18577. ISSN 2215-2075.
  9. ^ Jacobi Theodorie Klein naturalis dispositio Echinodermatum. Gleditsch.
  10. ^ Brustolin, Marco C.; Thomas, Micheli C.; Mafra, Luiz L.; Lana, Paulo da Cunha (2014-08-01). "Does Encope emarginata (Echinodermata: Echinoidea) affect spatial variation patterns of estuarine subtidal meiofauna and microphytobenthos?". Journal of Sea Research. 91: 70–78. doi:10.1016/j.seares.2014.03.006. ISSN 1385-1101.
  11. ^ a b Martinelli Filho, José Eduardo; dos Santos, Ronan Brito; Ribeiro, Caio Cesar (2014-07-01). "Host selection, host-use pattern and competition in Dissodactylus crinitichelis and Clypeasterophilus stebbingi (Brachyura: Pinnotheridae)". Symbiosis. 63 (3): 99–110. doi:10.1007/s13199-014-0292-0. ISSN 1878-7665. S2CID 256075356.
  12. ^ Guilherme, Pablo D. B.; Brustolin, Marco C.; Bueno, Maristela de L.; Guilherme, Pablo D. B.; Brustolin, Marco C.; Bueno, Maristela de L. (June 2015). "Distribution patterns of ectosymbiont crabs and their sand dollar hosts in a subtropical estuarine sandflat". Revista de Biología Tropical. 63: 209–220. doi:10.15517/rbt.v63i2.23155 (inactive 2023-08-31). ISSN 0034-7744.{{cite journal}}: CS1 maint: DOI inactive as of August 2023 (link)
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