Coccolith

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Scanning electron micrograph of Coccolithus
pelagicus, plated with coccoliths

Coccoliths are individual plates or scales of

coccosphere
.

Overview

Coccolithophores are spherical cells about 5–100 micrometres across, enclosed by calcareous plates called

coccoliths, which are about 2–25 micrometres across.[1]
Coccolithophores are an important group of about 200 marine phytoplankton species 
microzooplankton predation, which is one of the main causes of phytoplankton death in the ocean.[3]

  • Partial cross section of a coccolithophore with coccolith layer [4]
    Partial cross section of a coccolithophore with coccolith layer [4]
  • Coccolithophore cell surrounded by its shield of coccoliths. The coccolith-bearing cell is called the coccosphere.[5][6]
    Coccolithophore cell surrounded by its shield of coccoliths. The coccolith-bearing cell is called the coccosphere.[5][6]

Coccolithophores have been an integral part of

biological carbon pump and the oceanic uptake of atmospheric CO2.[3]

As of 2021, it is not known why coccolithophores calcify and how their ability to produce coccoliths is associated with their ecological success.

Heterotrophic protists are able to selectively choose prey on the basis of its size or shape and through chemical signals [27][28] and may thus favor other prey that is available and not protected by coccoliths.[3]

Formation and composition

Part of a series related to
Biomineralization
General
Exoskeletons (shells)
Endoskeletons (bones)
Teeth, scales, tusks etc
Calcification
Silicification
Other forms
Related

Coccoliths are formed within the cell in

Thomas Huxley was the first person to observe these forms in modern marine sediments and he gave them the name 'coccoliths' in a report published in 1858.[29][30]
Coccoliths are composed of calcium carbonate as the mineral
white cliffs of Dover (deposited in Cretaceous times), in which they were first described by Henry Clifton Sorby in 1861.[31]

Types

There are two main types of coccoliths, heterococcoliths and holococcoliths. Heterococcoliths are formed of a radial array of elaborately shaped crystal units. Holococcoliths are formed of minute (~0.1 micrometre) calcite

rhombohedra, arranged in continuous arrays. The two coccolith types were originally thought to be produced by different families of coccolithophores. Now, however, it is known through a mix of observations on field samples and laboratory cultures, that the two coccolith types are produced by the same species but at different life cycle phases. Heterococcoliths are produced in the diploid life-cycle phase and holococcoliths in the haploid phase. Both in field samples and laboratory cultures, there is the possibility of observing a cell covered by a combination of heterococcoliths and holococcoliths. This indicates the transition from the diploid to the haploid phase of the species. Such combination of coccoliths has been observed in field samples, with many of them coming from the Mediterranean.[32][33]

Types of coccoliths

Shape

Coccoliths are also classified depending on shape. Common shapes include:[34][35]

  • Calyptrolith – basket-shaped with openings near the base
  • Caneolith – disc- or bowl-shaped
  • Ceratolith – horseshoe or wishbone shaped
  • Cribrilith – disc-shaped, with numerous perforations in the central area
  • Cyrtolith – convex disc shaped, may with a projecting central process
  • Discolith – ellipsoidal with a raised rim, in some cases the high rim forms a vase or cup-like structure
  • Helicolith – a placolith with a spiral margin
  • Lopadolith – basket or cup-shaped with a high rim, opening distally
  • Pentalith – pentagonal shape composed of five four-sided crystals
  • Placolith – rim composed of two plates stacked on top of one another
  • Prismatolith – polygonal, may have perforations
  • Rhabdolith – a single plate with a club-shaped central process
  • Scapholith – rhombohedral, with parallel lines in center
Helicoliths of Helicosphaera carteri
Coccosphere of Emiliania huxleyi consisting of overlapping placoliths
  • Coccolith structures of representative Noelaerhabdaceae.[36] Each morphospecies is associated with a SEM image in the next diagram
    Coccolith structures of representative
    morphospecies
    is associated with a SEM image in the next diagram
  • SEM images correspond to coccolith drawings in the previous diagram (A) Gephyrocapsa ericsonii RCC4032 (B) Gephyrocapsa muellerae (C) Gephyrocapsa oceanica (D) Reticulofenestra parvular RCC4033; (E) Reticulofenestra parvular RCC4034; (F) Reticulofenestra parvular RCC4035; (G) Reticulofenestra parvular RCC4036; (H) Emiliania huxleyi morphotype R; (I) Emiliania huxleyi morphotype A; (J) Emiliania huxleyi morphotype B.
    SEM images correspond to coccolith drawings in the previous diagram
    (A) Gephyrocapsa ericsonii RCC4032 (B) Gephyrocapsa muellerae (C) Gephyrocapsa oceanica (D) Reticulofenestra parvular RCC4033; (E) Reticulofenestra parvular RCC4034; (F) Reticulofenestra parvular RCC4035; (G) Reticulofenestra parvular RCC4036; (H) Emiliania huxleyi morphotype R; (I) Emiliania huxleyi morphotype A; (J) Emiliania huxleyi morphotype B.

Function

Although coccoliths are remarkably elaborate structures whose formation is a complex product of cellular processes, their function is unclear. Hypotheses include defence against grazing by

UV
light; or in deep-dwelling species, to concentrate light for photosynthesis.

Fossil record

Because coccoliths are formed of low-Mg calcite, the most stable form of calcium carbonate, they are readily fossilised. They are found in sediments together with similar microfossils of uncertain affinities (nanoliths) from the

nannoplankton (nanoplankton)
.

References

  1. doi:10.1016/j.algal.2012.06.002
  2. doi:10.2113/gsmicropal.51.4.267
    .
  3. ^
    ISSN 2296-7745. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
    .
  4. ISSN 1932-6203. Modified material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
    .
  5. S2CID 6227548
    .
  6. ISSN 0377-8398
    .
  7. ISBN 978-3-642-06016-8
    .
  8. ISBN 978-3-642-06016-8
    .
  9. doi:10.1016/j.dsr2.2006.12.003
    .
  10. doi:10.1029/2009PA001731
    .
  11. S2CID 34159028
    .
  12. doi:10.1016/j.pocean.2007.11.003
    .
  13. hdl:2268/246251
    .
  14. ISBN 978-3-642-06016-8
    .
  15. ^ Young, J. R. (1987). Possible Functional Interpretations of Coccolith Morphology. New York: Springer-Verlag, 305–313.
  16. ^ Young, J. R. (1994). "Functions of coccoliths," in Coccolithophores, eds A. Winter and W. G. Siesser (Cambridge: Cambridge University Press), 63–82.
  17. hdl:10453/114799
    .
  18. ^
    PMID 27453937
    .
  19. doi:10.3389/fmars.2019.00049
    .
  20. ISBN 9780123705181
    .
  21. S2CID 21017882
    .
  22. PMID 30043404
    .
  23. doi:10.3389/fmars.2020.530757
    .
  24. S2CID 22995996
    .
  25. S2CID 135347218
    .
  26. ^ Young, J. R. (1994) "Functions of coccoliths". In: Coccolithophores, Eds A. Winter and W. G. Siesser (Cambridge: Cambridge University Press), 63–82.
  27. S2CID 36526359
    .
  28. doi:10.1093/plankt/fbq114
    .
  29. ^ Huxley, Thomas Henry (1858). "Appendix A". Deep Sea Soundings in the North Atlantic Ocean between Ireland and Newfoundland, made in H.M.S. Cyclops, Lieut.-Commander Joseph Dayman, in June and July 1857. London: British Admiralty. pp. 63–68 [64].
  30. ^ Huxley, Thomas Henry (1868). "On some organisms living at great depth in the North Atlantic Ocean". Quarterly Journal of Microscopical Science. New series. 8: 203–212.
  31. doi:10.1080/00222936108697404
    .
  32. ISSN 1886-8134
    .
  33. ISBN 978-960-411-660-7
    .
  34. ISBN 978-0-521-03169-1
    .
  35. ISBN 978-0-323-13827-7
    .
  36. ISSN 1664-302X. Modified material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
    .

External links

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