Acarinina collactea

Classification: pf_cenozoic -> muricate non-spinose -> Truncorotaloididae -> Acarinina -> Acarinina collactea
Sister taxa: A. medizzai, A. collactea, A. pentacamerata, A. aspensis, A. echinata, A. pseudosubsphaerica, A. alticonica, A. soldadoensis, A. interposita, A. cuneicamerata, A. angulosa, A. africana, A. sibaiyaensis, A. esnehensis, A. mckannai, A. subsphaerica, > >>


Citation: Acarinina collactea (Finlay 1939)
Rank: Species
Basionym: Globorotalia collactea
Taxonomic discussion: This is one of the most distinct and ubiquitous components of middle Eocene planktonic foraminiferal assemblages. Distinguished by its small size and compact, densely muricate test with irregularly distributed minute “openings” on the spiral side, it is a familiar and particularly common form in mid-high latitude assemblages.
This form has been thoroughly studied and documented by Jenkins (1965a) who re-examined Finlay’s original type material. Blow (1979, p. 920) noted that the suturally-located openings on the spiral side do not appear to be functional supplementary apertures and may owe their origin to the “stand off” effect of late stage calcification preventing smooth junction of adjacent chambers owing to the development of previously calcified muricae in the intervening space(s).
The form identified by Bolli (1957a) as Globorotalia spinuloinflata (Bandy) is a subangular variant of the generally more rounded collactea and included here in the synonomy of collactea. In the former Soviet Union collactea has been identified as Acarinina rotundimarginata Subbotina from the middle Eocene of the N. Caucasus. We specifically exclude from collactea the ovate, sinistrally coiled specimens identified by Bronnimann (1952) and Postuma (1971) from the lower Eocene (Zone P6b) of Trinidad. Acarinina collactea is generally subcircular in outline, dextrally coiled and restricted to stratigraphically younger levels. The possible extension of this taxon into upper Eocene levels in high latitudes remains controversial. [Berggren et al. 2006]

Catalog entries: Acarinina rotundimarginata;
Globorotalia collactea;

Type images:

Distinguishing features: This taxon is distinguished by its small size (~0.25-0.30 mm in maximum diameter), 5-chambered and compact (involute) test. Acarinina medizzai is morphologically similar to, and probably descended from, A. collactea. The moderately muricate medizzai may be distinguished from collactea in having a smaller (generally less than 0.2 mm in diameter), lower trochospiral test and more restricted aperture.

NB The short diagnoses are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus. They have initially been copied from the diagnostic characters/distinguishing features sections of the Eocene and Paleocene Atlases, they will be edited as the site is developed.


Diagnostic characters: This taxon is distinguished by its small size (~0.25-0.30 mm in maximum diameter), 5-chambered and compact (involute) test. Acarinina medizzai is morphologically similar to, and probably descended from, A. collactea. The moderately muricate medizzai may be distinguished from collactea in having a smaller (generally less than 0.2 mm in diameter), lower trochospiral test and more restricted aperture. [Berggren et al. 2006]

Wall type: Nonspinose; normal perforate; densely muricate on both sides. [Berggren et al. 2006]

Test morphology: Test low-trochospiral, 5 subangular, essentially equal sized chambers in last whorl, separated by straight radial to weakly curved intercameral sutures; umbilicus narrow, deep; aperture a low, arched slit along the base of the last chamber; weakly convex to flat; about 12 rounded chambers in three whorls on the spiral side; sutures radial, straight to weakly curved; minute intercameral openings visible at chamber junction margins on some well-preserved specimens; rounded to subangular peripheral margin in edge view. [Berggren et al. 2006]

Size: Maximum diameter of holotype 0.18 mm, thickness 0.13 mm. [Berggren et al. 2006]

Character matrix

test outline:-chamber arrangement:Trochospiraledge view:-aperture:-
umb chamber shape:-coiling axis:Lowperiphery:N/Aaperture border:N/A
sp chbr shape:-umbilicus:Narrowperiph margin shape:Subangularaccessory apertures:-
umbilical or test sutures:-umb depth:Deepwall texture:-shell porosity:Finely Perforate: 1-2.5µm
spiral sutures:-diameter mm:0.18width mm:breadth mm:0.13
final-whorl chambers:4.5-5.5

Biogeography and Palaeobiology

Geographic distribution: As the synonymy given above indicates, this taxon has an essentially
cosmopolitan distribution, having been recorded from latitudes in excess of 50o in both the northern (Denmark, NW Germany) and southern (Kerguelen Plateau and Maud Rise) hemispheres. [Berggren et al. 2006]
Aze et al. 2011 summary: Cosmopolitan; based on Berggren et al. (2006b)

Isotope paleobiology: No data available. [Berggren et al. 2006]
Aze et al. 2011 ecogroup 1 - Open ocean mixed-layer tropical/subtropical, with symbionts. Based on very heavy δ13C and relatively light δ18O. Sources cited by Aze et al. 2011 (appendix S3): Pearson et al. (1993, 2001a)

Phylogenetic relations: Ancestry uncertain; possibly descended from A. pentacamerata; this morphospecies probably evolved into A. medizzai. [Berggren et al. 2006]

Most likely ancestor: Acarinina pentacamerata - at confidence level 4 (out of 5). Data source: Berggren et al. (2006) fig9.2.

Biostratigraphic distribution

Geological Range:
Notes: Zone E7 to Zone E14. On the Kerguelen Plateau collactea disappears at a stratigraphic level possibly correlative with Magnetochron C17n (~/= to Zones NP17/18=P15; ~ 37 Ma; near the Bartonian/Priabonian = middle/late Eocene boundary; Berggren, 1992, p. 556, 557). Earlier, the record from the Søvind Marl in Denmark (Berggren, 1969) suggested extension to the Priabonian/late Eocene (Isthmolithus recurvus Zone =NP19/20). [Berggren et al. 2006]
Last occurrence (top): within E15 zone (34.68-35.89Ma, top in Priabonian stage). Data source: Eocene Atlas
First occurrence (base): within E7a subzone (48.31-50.20Ma, base in Ypresian stage). Data source: Eocene Atlas

Plot of occurrence data:

Primary source for this page: Berggren et al. 2006 - Atlas of Eocene Planktonic Foraminifera, chapter 9, p. 276


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Acarinina collactea compiled by the pforams@mikrotax project team viewed: 22-3-2018

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