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Current identification:
Original Description
Size:
Extra details from original publication
Derivation of name. Refers to the variabile height of the spire.
Occurence. Zones P4a–P5 (basal part).
Geographic distribution. This species has been recorded at low and mid latitudes and it is present in (sub)tropical assemblages from the Atlantic and Pacific Oceans.
Remarks. In our samples this taxon is abundant in Zone P4 (sub)tropical assemblages of Pacific Ocean (Holes 1209B and 865B). Generally, this species is characterized by having a moderately to strongly biconvex test and a circular profile. Typical forms of Igorina paraspiralis n. sp. have been reported and illustrated by Blow (1979) in Zone P5 from the Atlantic province. However, we have observed this species to have a wide range of morphologic variation. Some specimens are characterized by a trochospire that projects up to 2/3 the total length of the entire shell. A similar morphotype was illustrated by Olsson and others (1999) from the Vincentown Formation (Glendola Well, New Jersey). Moreover, in Subzone P4b assemblages, we have observed rare morphotypes that display a thicker test with a shorter but wider spire and with a broadly arched aperture on the last chamber. The latter forms usually display 8–9 (rarely 10) chambers of almost equal size in the last whorl. Igorina paraspiralis is distinguished from all the other igorinids by the large number of chambers visible on its spiral side. Our phylogenetic analysis suggests that this form probably evolved from I. albeari in Subzone P4a. Its highest occurrence is in the lower part of Zone P5.
Distinguishing features. Igorina paraspiralis is distinguished from I. albeari in having a more-subrounded peripheral margin and lack a carinate last chamber.
Soldan, D. M., Petrizzo, M. R., Silva, I. P. & Cau, A. (2011). Phylogenetic relationships and evolutionary history of the Paleogene genus through parsimony analysis. Journal of Foraminiferal Research. 41: 260-284. gsReferences:
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Igorina paraspiralis compiled by the pforams@mikrotax project team viewed: 9-6-2023
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