Carterinida is an order of multi-chambered

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular Ectoplasm (cell biology), ectoplasm for catching food and ot ...

within the

Globothalamea Globothalamea comprises a class of multichambered foraminifera based in part on SSU rDNA evidence; the other is Tubothalamea. Six orders are included, which vary notably in composition, wall structure, and chamber arrangement. The Lituolida, L ...

. Members of this order form hard tests out of thin

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

rods known as spicules, which are held together by a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

aceous matrix. The spicules of carterinids have been a source of debate; as they are held together by a protein matrix, it has been suggested that the test is created by agglutinating spicules from the

amoebozoa Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported classi ...

n '' Trichosphaerium''. However, life observations of carterinids have failed to find evidence of agglutination, and members of the group have been found to grow on artificial substrates where such spicules were not available from the environment. This suggests the spicules are instead created by the carterinids themselves. The spicules of carterinids are formed of low-magnesium calcite and have "blebs" of organic matter within. Two sizes of spicules are present; smaller spicules are packed tightly between the larger spicules. Spicules appear to have been produced within the cell and moved to their position, as they are rounded and adjacent spicules are not connected. Carterinids were long considered to be represented by a single genus, '' Carterina''. However, the genus '' Zaninettia'' was described in 1983 as a second carterinid genus characterised by the presence of secondary septa. This was not unanimously accepted by all researchers; however, a 2014 genetic study found two species of ''Zaninettia'' to form distinct genetic groups closely related to ''Carterina''. This study also found Carterinida to be a distinct group within the Globothalamea, and identified several unnamed " Trochamminids" as likely members of the clade. ''Carterina'' and ''Zaninettia'' can be further distinguished by the shape of their spicules: those of ''Carterina'' are ovoid in cross-section, while those of ''Zaninettia'' are "rounded-rectangular". Fossils of Carterinids (specifically ''Carterina'') from the Ceara and Potiguar basins off the coast of

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

date back to the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

, and possibly to the

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

References

Foraminifera Foraminifera orders Globothalamea {{Foraminifera-stub