Catalog - Globorotalia (Acarinina) appressocamerata

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Globorotalia (Acarinina) appressocamerata

Citation: Globorotalia (Acarinina) appressocamerata Blow 1979

Type locality: DSDP Site 20C, core 5, sect. 4 between 77 and 79 cm, in 4506 m of water at lat. 28 0 31.47' S. , long. 260 50.73' W. , central South Atlantic on the west flank of the Mid-Atlantic Ridge.

Type age (chronostrat): Middle Lower Eocene, middle Cuisian [Ypresian], Subzone P8b (upper Globorotalia aragonensis zone); ranges up to Zone P9, upper Lower Eocene.

Type specimens: Paratype PM PF 64344

Original Description
The test is comprised of about 11-12 chambers coiled in a low trochospire with five chambers present in the last convolution of the test. The coiling mode is tight with the chambers close appressed and embracing. In dorsal aspect, the chambers are longer tangentially (anterior-posteriorly) than radially broad with the dorsal intercameral sutures sub-radially or slightly sinuously disposed; the spiral and intercameral, sutures are slightly incised between only slightly inflated chambers. The equatorial profile is only slightly lobate, sensibly smoothly rounded. The chambers do not increase rapidly as added in the pregression of the trochospire. In axial-apertural view the chambers are lunate in plan, rounded without any peripheral angularity. In ventral aspect the umbilicus is small but open and deep. The primary aperture extends from the umbilicus to about 1/3 of the way along the basal suture of the final chamber to the periphery. The primary aperture is bordered by a distinct lip and is a low arched opening.The umbilicus contains the relict apertures of the later chambers of the last convolution which open directly into the umbilical depression. The ventral sutures are radially disposed but only slightly incised. The walls of the chambers, especially on the ventral surfaces around the umbilicus, are muricate.

Size: Maximum diameter of holotype 0.37 mm.

Extra details from original publication
This variation associated with the writer's new taxon is shown on pl. 144. The paratype illustrated in fig. 9 shows a morphotype with a particularly tight coiling-mode and small umbilicus whilst the paratype illustrated in fig. 6 shows a morphotype at the other end of the spread of variation showing a looser coilingmode, more open umbilicus and less appressed and embracing chambers. The extreme of variation seen in fig. 6 is also accompanied by some migration of the aperture towards a more nearly intraumbilical position reminiscent of the condition seen in Muricoglobigerina. This trend is also seen in the form recorded as Globorotalia (Acarinina) cf. appressocamerata (Blow, 1979, op. cit., pl. 144, fig. l) where the muricoglobigerinid trend is even better developed.
The morphotype recorded as G. (A.) cf. appressocamerata (Blow, 1979, OP• pl. 144, fig. 3) similarly shows a somewhat looser coiling-mode but shows chambers which increase in size rather more rapidly as added in the progression of the trochospire combined with some decrease of the number of chambers in the last convolution of the test.
Although Globorotalia (Acarinina) appressocamerata Blow, 1979, shows features similar to those seen in G. (A.) subsphaerica (Subbotina) [Acarinina subsphaerica, 1953], Subbotina's taxon disappears from the geohistoric record in Zone P .5 whilst G. (A.) appressocamerata Blow, 1979, does not appear until the base of Subzone P.8b and no connecting morphotypes have been observed. The main morphological differences between appressocamerata and subsphaerica lie in the slightly more angulate chambers in ventral aspect of the former taxon as compared to the rounded chambers of subsphaerica. Furthermore, in appressocamerata Blow, 1979, the umbilicus is quadrate in outline, sharply delimited and usually more widely open than in G. (A.) subsphaerica Subbotina.

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. gs V O

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

CATALOG OF ORIGINAL DESCRIPTIONS: Globorotalia (Acarinina) appressocamerata Blow 1979

Globorotalia (Acarinina) appressocamerata

References:

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