This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.
Linked specimens: London, UK; NHM (PM PF 64570) London, UK; NHM (64714)
Current identification/main database link: Acarinina praetopilensis (Blow 1979)
The moderately large test is coiled in a low trochospire with about 9-10 chambers comprising the spire and four chambers in the last whorl. In dorsal aspect, the chambers are considerably longer tangentially than radially broad and with the anterior and posterior margins of the last chamber laterally compressed to give a mitriform appearance to this final chamber. The lateral angulation is only seen for the last two chambers and the earlier chambers of the final convolution of the test are lunate to hemispherical in dorsal aspect and even the penultimate chamber is not distinctly disjunct. The last chamber is, however, distinctly disjunct with the peripheral margin of the chamber flattened to appear only slightly inflated, The peripheral flattening of the last chamber gives rise to a circumcamerally subacute to acute margin to the chamber and this margin bears a circumcameral, ring-like, concentration of muricae which, in part at least, are fused together to give a muricocarinal structure. The penultimate chamber also shows a little peripheral flattening but not to the extent as the last chamber whilst all the earlier chambers are not so flattened but remain inflated. Whilst there is a concentration of muricae along the peripheral margin of the penultimate chamber there is no ring-like organisation of the muricae into a circum-cameral muricocarina; there is neither a circum-cameral concentration of muricae nor a muricocarlna on any of the earlier chambers of the last whorl prior to the last one. The penultimate chamber is not distinctly disjunct with respect to the preceeding antepenultimate chamber but the ventral intercameral sutures are quite deeply incised for all the chambers of the final convolution. The dorsal side of the test possesses two supplementary apertures which are bordered by rim-like margins on their distal margins suggesting that these openings were true functional supplementary apertures. The umbilicus is open and deep and the rimmed primary aperture extends from the umbilicus to about half way towards the periphery. The wall of the test is muricate and some at least of these muricae are known to be hollow structures (see remarks below).
Size: Maximum diameter of holotype, 0.38 mm.
Extra details from original publication
The paratype specimens figured on pl. 169, figs. 4 and 7, were chosen to compare very closely with the holotype (pl. 169, fig. 8) notwithstanding their opposite coiling direction. These two paratypes show the axial-apertural view (fig. 4) and dorsal view (fig. 7) of typical specimens of Globorotalia (Truncorotaloides) topilensis praetopilensis Blow, 1979. From these specimens and the holotype it can be seen that the taxon is characterised by the distinctly disjunct last chamber which is separated for about one half of the radial breadth of the chamber from the antepenultimate chamber. The axial-apertural view of the paratype in figure 4 also shows clearly the peripheral flattening of the final chamber and the circum-cameral concentration of partially fused and coalesced muricae which forms a muricocarina. Plate 208, figs. 1-4, show details of some of the muricae most of which can be seen to be hollow structures. Plate 208, fig. 5, also shows details of the supplementary aperture shown in the base of the last chamber of the paratype figured on pl. 196, fig. 7; from this photograph it can be seen that the supplementary aperture is bordered by a narrow area of imperforate, nonmurycate test material which forms a slightly raised rim to the opening . the writer considers that this rim-like feature differentiates between truly functional supplementary apertures and the more-or-less randomly situated adventitious dorsal openings seen in many acarininid and morozovellid taxa.
Two specimens (Blow, 1979, op. cit., pl. 154, figs. 8 and 9) are considered as specimens ex interc Globorotalia (Acarinina) pseudotopilensis (Subbotina) [Acarinina pseudotopilensis, 1953] and Globorotalia (Truncorotaloides) topilensis praetopilensis. These two specimens appear to show the derivation of praetopilensis from pseudotopilensis, which appears to occur by the increasing lateral compression of the posterior and anterior margins of the last chamber so that this chamber becomes laterally angulate. The paratypic specimen of praetopilensis illustrated on pl. 155, fig. 9, is considered phylogenetically primitive but does show the separation of the last chamber and the development of a circum-cameral concentration of muricae around the margin of the somewhat disjunct final chamber. However, the umbilicus of this paratype remains small and the earlier test, especially, retains features usually seen in Subbotina's taxon pseudotopilensis. Thus, this specimen possesses the more tightly expressed coiling-mode and the more closely appressed earlier chambers of the last 1 1
convolution as seen in pseudolopilensis but combines these features with the more disjunct, laterally angulate, ultimate and penultimate chambers typical of praetopilensis. The nature of the apertural system of this phylogenetically primitive paratypic specimen of G. (Truncorotaloides) topilenois praetopilensis is examined in detail on pl. 203, fig. l; furthermore, the circum-cameral concentration of muricae on the last chamber of this specimen is also examined on pl. 203, fig. 2, where it can be seen that there is some partial fusion of the muricae to give a circum-cameral muricocarina. This is a feature not seen in pseudotopilensis (see Blow, 1979, op. cit., p. 956) and explains why the specimen is referred to the writer's new taxon praetopilensis notwithstanding the closely appressed earlier chambers of the last convolution of the test.
"The paratypes of praetopilensis illustrated on pl. 178, figs. 6-9, are considered to be typical representatives of the new taxon but the specimens illustrated on pl. 185, figs. 7-8, and pl. 187, figs. 1-4, are considered as phylogenetically advanced representatives of praetopilensis which show transition to topilensis topilensis (Cushman) [Globigerina topilensis, 1925]. These phylogenetically advanced specimens still retain the comparatively small umbilicus of praetopilensis but show the complete fusion of the circum-cameral muricae to give a continuously expressed circum-cameral muricocarina (cf. pl. 207, figs. I and 2 with pl. 207, figs. 5 and 6). In summary, G. (T.) topilensis praetopilensis differs from G. (T.) topilensis topilensis (Cushman) by possessing a tighter coiling-mode, a smaller umbilicus, and muncocarinal development which usually only appears on the last chamber or on the last two chambers in morphologically advanced forms. Furthermore, in praetopilensis the later chambers of the last convolution of the test are not so disjunctly set in the progression of the trochospire as they are in topilensis topilensis (Cushman). Finally, the dorsal supplementary apertures in praetopilensis are not so large or numerous as in topilensis (sensu stricto)."
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 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
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
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
Globorotalia (Truncorotaloides) topilensis praetopilensis compiled by the pforams@mikrotax project team viewed: 24-1-2020
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