Acarininainterposita Subbotina, 1953:231, pl. 23: figs. 6a-c [holotype, lower Eocene Zone of conical globorotaliids, Khieu River section, Nal’chik region, northern Caucasus]; figs. 7a-c [lower Eocene Zone of conical globorotaliids, Kuban River section, northern Caucasus].— Krasheninnikov and others, 1988:96, pl. 8: figs. 4-6 [G. aragonensis Zone, DSDP Site 277, Campbell Plateau].
Globorotalia (Acarinina) interposita (Subbotina).—Blow, 1979:931-933, pl. 156: figs. 7-9 [Zone P10, piston core Kane 9-C, North Atlantic Ocean].
?Acarininainterposita Subbotina, 1953.—Stott and Kennett, 1990:559, pl. 6: figs. 3,4 [Zone AP9, ODP Hole 689B, Maud Rise, southern South Atlantic Ocean].—Huber, 1991:439, pl. 2: figs. 13-15 [Zone AP7, ODP Site 738, Kerguelen Plateau, southern Indian Ocean].—Lu and Keller, 1993:119, pl. 2: figs. 9, 11 [Zone AP5, ODP Hole 738C, Kerguelen Plateau, southern Indian Ocean].
Taxonomic discussion: This distinctly inflated (globular) form is characteristic of lower Eocene assemblages; it is predominantly dextrally coiled throughout its range. We have observed it to appear in Zone E4 in Egypt and to grade into A. pentacamerata at stratigraphically higher/ younger levels. We question the high latitude records of forms cited under this name (see synonymy listing above); they do not appear to display the robust, inflated morphology characteristic of low latitude representatives, and indeed some of the forms are recorded from distinctly lower stratigraphic levels (Zone AP5 [which approximately correlates with Zone E2]) and contain only 3 chambers in the final whorl (Lu and Keller, 1993). [Berggren et al. 2006]
Distinguishing features: Parent taxon (Acarinina): Moderate to low trochospire; chambers ovoid, usually 4-6 in final whorl. Wall muricate with pustules on umbilical shoulders; This taxon: Test with 4-4½ chambers in the final whorl, planoconvex with scalloped, lobulate peripheral margin; distinctly muricate; chambers umbilically inflated
NB These concise distinguishing features statements are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus. They are being edited as the site is developed and comments on them are especially welcome.
Description
Diagnostic characters: This taxon is distinguished by its 4-4½ chambers (in the final whorl), planoconvex, distinctly muricate, test with umbilically inflated (globular) chambers; umbilical side of test distinctly inflated, accompanied by loose arrangement of chambers resulting in scalloped, lobulate peripheral margin. [Berggren et al. 2006] Morphology: Low-trochospiral; relatively large, robust, test with embracing, appressed chambers; plano-convex, weakly lobate, circular outline, rounded periphery in edge view; 4-4½ chambers in final whorl, increasing slowly in size, generally globular; sutures depressed, radial, weakly curved; muricae more strongly developed on umbilical than on spiral side, short, thick muricae concentrated around umbilicus, which is narrow, deep; about 10-12 chambers in 2-3 whorls on spiral side; early chambers obscured by muricate texture, chambers of final whorl increasing slowly in size, essentially equidimensional; sutures radial, straight, only slightly depressed; muricae tend to concentrate along peripheral margin; in edge view planoconvex; profile of early chambers rounded, with flattening of ante- and/or penultimate chamber resulting in subacute margin; peripheral margin; aperture an umbilical-extraumbilical arch, bordered by thin lip, extending almost to peripheral margin. [Berggren et al. 2006] Wall type: Densely muricate on both sides, non-spinose; normal perforate. [Berggren et al. 2006] Size: Diameter 0.35-0.55 mm, thickness 0.20-0.25 mm. [Berggren et al. 2006]
Character matrix
test outline:
Subcircular
chamber arrangement:
Trochospiral
edge view:
Planoconvex
aperture:
Umbilical-extraumbilical
sp chamber shape:
Globular
coiling axis:
Low
periphery:
N/A
aperture border:
Thin lip
umb chbr shape:
Globular
umbilicus:
Narrow
periph margin shape:
Broadly rounded
accessory apertures:
None
spiral sutures:
Weakly depressed
umb depth:
Deep
wall texture:
Coarsely muricate
shell porosity:
Finely Perforate: 1-2.5µm
umbilical or test sutures:
Weakly depressed
final-whorl chambers:
4-4.5
N.B. These characters are used for advanced search. N/A - not applicable
Biogeography and Palaeobiology
Geographic distributionOccurs commonly in the Tethys (Egypt) and in the northern Caucasus. [Berggren et al. 2006]
Aze et al. 2011 summary: Tethys (Egypt) and in the northern Caucasus; based on Berggren et al. (2006b) Isotope paleobiologyNo data available. [Berggren et al. 2006] Aze et al. 2011 ecogroup 1 - Open ocean mixed-layer tropical/subtropical, with symbionts; based on comparison with other species of the genus. Phylogenetic relationsThis taxon seems to have been derived from A. soldadoensis and evolved into A. pentacamerata by an increase in the number of chambers in the whorl and a change in the spire height. [Berggren et al. 2006]
Geological Range: Notes: Zone E4 to Zone E6. [Berggren et al. 2006] Last occurrence (top): within E6 zone (50.20-50.67Ma, top in Ypresian stage). Data source: Eocene Atlas First occurrence (base): within E4 zone (52.54-54.61Ma, base in Ypresian stage). Data source: Eocene Atlas
Plot of occurrence data:
Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
Triangles indicate an event for which a precise placement has been suggested.
Grey shading between taxa indicates intergrading species within an anagenetic lineage (data from
Lamyman et al. 2026).
(NB There is no histogram as there are no occurrence records for the taxon in the Neptune database) Parent: Acarinina
Primary source for this page: Berggren et al. 2006 - Eocene Atlas, chap. 9, p. 290
References:
Berggren, W. A., Pearson, P. N., Huber, B. T. & Wade, B. S. (2006b). Taxonomy, biostratigraphy, and phylogeny of Eocene Acarinina. In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 41(Chap 9): 257-326. gsO
Blow, W. H. (1979). The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and stratigraphical distribution of some Globigerinida (mainly Globigerinacea). E. J. Brill, Leiden. 2: 1-1413. gs
Huber, B. T. (1991c). Paleogene and Early Neogene Planktonic Foraminifer Biostratigraphy of Sites 738 and 744, Kerguelen Plateau (Southern Indian Ocean). Proceedings of the Ocean Drilling Program, Scientific Results. 119: 427-449. gs
Krasheninnikov, V. A., Serova, M. Y. & Basov, I. A. (1988). Stratigrafiya I planktonnyie foraminiferyi paleogena: vyisokikh shirot Tikhogo okeana. Trudy Geologicheskiy Institut Akademiya Nauk SSSR. 429: 1-120. gs
Lu, G. & Keller, G. (1993). The Paleocene-Eocene transition in the Antarctic Indian Ocean: Inference from planktic foraminifera. Marine Micropaleontology. 21: 101-142. gs
Stott, L. D. & Kennett, J. P. (1990). The Paleoceanographic and Paleoclimatic signature of the Cretaceous/Paleogene boundary in the Antarctic: Stable isotopic results from ODP Leg 113. Proceedings of the Ocean Drilling Program, Scientific Results. 113: 829-848. gs
Subbotina, N. N. (1953). Foraminiferes fossiles d'URSS Globigerinidae, Globorotaliidae, Hantkeninidae. Bureau de Recherches Geologiques et Minieres. 2239: 1-144. gs
Acarinina interposita compiled by the pforams@mikrotax project teamviewed: 15-9-2026
Eocene_Atlas_pl09-11_fig17-19.jpg
Eocene_Atlas_pl09-11_fig16.jpg
Eocene_Atlas_pl09-11_fig17-19.jpg
Eocene_Atlas_pl09-11_fig16.jpg
paratype: A. interposita
