Globigerinoides

Globigerinoides is an extant genus of shallow-water planktonic foraminifera of family Globigerinidae.[1] First appearing in the Oligocene these foraminifera are found in all modern oceans. Species of this genus occupy the euphotic zone, generally at depths between 10-50m, in waters which cover a range of salinities and temperatures.[2] They are a shorter lived species, especially when compared to Globorotalia genus.[2] As a genus Globigerinoides is widely used in various fields of research including biostratigraphy, isotope geochemistry, biogeochemistry, climatology, and oceanography.

Globigerinoides
Scientific classification
(unranked):	SAR
(unranked):	Rhizaria
Phylum:	Foraminifera
Class:	Polythalamea
Order:	Rotaliida
Suborder:	Globigerinina
Superfamily:	Globigerinoidea
Family:	Globigerinidae
Genus:	Globigerinoides Cushman, 1927
Type species
Globigerina rubra d'Orbigny, 1839
Species
Globigerinoides altiaperturus Globigerinoides apertasuturalis Globigerinoides bispherica Globigerinoides bisphericus Globigerinoides conglobatus Globigerinoides elongatus Globigerinoides gomitulus Globigerinoides hyalinus Globigerinoides inusitatus Globigerinoides minuta Globigerinoides pyramidalis Globigerinoides quadrilobatus Globigerinoides ruber Globigerinoides sacculifer Globigerinoides sicanus Globigerinoides tenella Globigerinoides trilobus

Morphology

The foraminifera of genus Globigerinoides are all shallow-water species with spinose forms made of hyaline calcite.[2] Most species have trochospiral chamber arrangement, though some species exhibit further complexity with streptospiral chamber arrangement. Tests are composed of thin perforated walls, with very large pores, and spines being added at the end of individual chamber formation.[2][3] Certain species are known to produce a modified type of calcium carbonate, ¹⁸O enriched-gametogenic calcite, at the end of their life cycle. Prior to gametogenesis and the production of the final calcite layer, the spines are reabsorbed by the foraminifera leaving behind a test that is heavily calcified, and shows the remnants of spine holes.[2][4] As with other amoeboids these foraminifera utilize pseudopodia. Pseudopodia are widely used throughout their entire lifecycle for various purposes including feeding, movement, protection, and chamber formation.

Symbionts

Many Globigerinoides species bear photosynthetic symbiotic algae. The relationship between the symbiotic algae and its host foraminifera provides the host with at least three main advantages, including energy from photosynthesis, an enhancement of calcification, and uptake of host metabolites. All in all it is a prime example of ectosymbiosis.[2] For those species that bear symbiotic algae, experiments have shown that their symbionts play a hugely important role in the success of individual foraminifera. Experiments using Globigerinoides sacculifer found that the life cycle of individuals is severely shorted when the symbionts photosynthetic cycle is disrupted or stopped (via darkness or removal of symbionts).[5]

Notable species

Certain species of Globigerinoides are more commonly used in various types of research than others. Commonly used species include G. ruber,G. sacculifer, G. subquadratus, and G. altiaperturus.

Globigerinoides sacculifer

Globigerinoides sacculifer exhibits two different morphologies, known as G. sacculifer with sac and G. sacculifer without sac. The sac feature is a sac shaped terminal chamber that is formed prior to the production of the gametogenic calcite. When using G. sacculifer tests for bulk isotope analysis tests without the sac morphology are often preferentially selected.[4] G. sacculifer is also notable for certain in vivo experiments that have been conducted on it. It was found that individuals of this species are able to reconstruct their tests after injury when subjected to slight crushing in a laboratory setting. These repaired tests would often have nonstandard morphologies.[6]

Globigerinoides ruber

Globigerinoides ruber are carnivorous and prey upon copepods and nauplii. Once a copepod or nauplii is caught in its spines G. ruber uses its pseudopodia to draw the caught prey close to its test to allow it to feed.[2] Also notable about G. ruber is its two morphologies, a form with pink tests, and a form with whitish tests. White test individuals are found today in warm to temperate climate zones of the Atlantic, Pacific, and Indian Oceans, where as pink tested G. ruber is now only found in the Atlantic Ocean. It is unknown why the pink individuals are no longer found in the Pacific and Indian Oceans, but this variety disappeared from those oceans ~120,000 yr.[7]G. ruber has been found to tolerate hyposaline waters, in laboratory cultures it was able to remain alive in salinity ranges of 22-49%.[8]

Globigerinoides subquadratus

Among other microfossil evidence, the last common occurrence of G. subquadratus is defined as the beginning of the Tortonian stage of the geologic time scale. The boundary is defined at the Monte dei Corvi Beach section in Italy.[9]

Globigerinoides altiaperturus

The first appearance datum of G. altiaperturus is the proposed base of the Burdigalian stage of the geologic time scale. The boundary has not yet been defined with a GSSP by the International Commission on Stratigraphy.[10]

References

1. Hayward, B. W.; Cedhagen, T.; Kaminski, M.; Gross, O. (2013). "Globigerinoides Cushman, 1927". World Foraminifera Database. Retrieved 2013-11-05.
2. Gupta, Barun K. Sen (2003). Modern Foraminifera. Kluwer Academic Publishers. pp. 15, 19, 24, 32, 48, 108–122, 245–247. ISBN 0-412-82430-2.
3. Hemleben, CH; Erson, OR; Berthold, W & Spindler, M (1986). BSC Leadbeater & R Riding (eds.). "Calcification and chamber formation in Foraminifera-a brief overview". Biomineralization in lower plants and animals, Clarendon Press, Oxford: 237–249.
4. Spero, Howard J; Lea, David W (1993). "Intraspecific stable isotope variability in the planktic foraminifera Globigerinoides sacculifer: Results from laboratory experiments". Marine Micropaleontology. 22: 221–234. doi:10.1016/0377-8398(93)90045-y.
5. Bé, A.W.H.; Spero, H.J. & Anderson, O.R. (1982). "Effects of symbiont elimination and reinfection on the life processes of the planktonic foraminifer Globigerinoides sacculifer". Marine Biology. 70: 73–86. doi:10.1007/bf00397298.
6. Bé, A.W.H.; Spero, H.J (1981). "Shell regeneration and biological recovery of planktonic foraminifera after physical injury induced in laboratory culture". Micropaleontology: 305–316.
7. Thompson, Peter R; Be, Allan WH; Duplessy, Jean-Claude & Shackleton, Nicholas J (1979). "Disappearance of pink-pigmented Globigerinoides ruber at 120,000 yr BP in the Indian and Pacific Oceans". Nature. doi:10.1038/280554a0.
8. Be, A.W.H; Tolderund, D.S. (1971). "Distribution and ecology of living planktonic foraminifera in surface waters of the Atlantic and Indian Oceans". The Micropalaeontology of Oceans: 103–149.
9. Ogg, Gabi. "GSSP for Tortonian Stage". Geologic Timescale Foundation. Retrieved 8 November 2013.
10. Ogg, Gabi. "GSSP Table - Cenozoic Era". Geologic Timescale Foundation. Retrieved 8 November 2013.