Catalog - Igorina paraspiralis

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Other pages this level: I. isabellae, I. paraspiralis, I. praecarinata

Igorina paraspiralis

Citation: Igorina paraspiralis Soldan, Petrizzo, Premoli Silva, & Cau 2011

Type specimens: Holotype (Micro-Unimi no. 1980); paratypes 1 and 2 (Micro-Unimi no. 1981 and 1982, respectively)

Type sample (& lithostrat): 198-1209B-22H-4, 101–102 cm

Type age (chronostrat): Paleocene

Type locality: Shatsky Rise ODP site 1209B (32.65N; 158.51E)

Type repository: Milan; Micropaleontological Collection, Universita degli Studi di Milano, Dipartimento di Scienze della Terra ÔÔA. DesioÕÕ, Italy.

Test small to medium sized, subcircular to circular, almost compact outline, asymetrically biconvex with a moderate to very prominent high spire and slightly convex umbilical side; peripheral margin ranging from broadly rounded to slightly subangular, surface texture pustulose; umbilical side with 9–10 essentially equidimen- sional triangular chambers, sutures straight radial, umbili- cus small, narrow, and deep; spiral side with three whorls tightly coiled with 7–8 (rarely 9–10) chambers in the final whorl, increasing very slowly in the size as added, sutures strongly recurved and weakly incised; aperture an inter- iomarginal, umbilical-extraumbilical, moderately high arch extending nearly to the periphery.

Diameter 0.26 mm; thickness 0.19 mm.

Globorotalia (Acarinina) convexa cf. convexa (Subbotina) in Blow, 1979, pl. 100, figs. 1, 2, 4.
Globorotalia (Acarinina) convexa convexa (Subbotina) in Blow, 1979, pl. 100, figs. 5–9.
Igorina pusilla (Bolli) in Olsson and others, 1999, p. 70, pl. 57, figs. 6–8.
Igorina pusilla ‘‘high trochospire’’ (Bolli) in Petrizzo, 2005, p. 29, pl. 4, figs. 6a–c, 9a–c.

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.

References:

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. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Igorina paraspiralis Soldan, Petrizzo, Premoli Silva, & Cau 2011

Igorina paraspiralis

References:

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