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

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.


Higher levels: pf_cat -> G -> Globorotalia (Acarinina) -> Globorotalia (Acarinina) praeaequa
Other pages this level: G. (Acarinina) appressocamerata, G. (Acarinina) broedermanni anapetes, G. (Acarinina) cuneicamerata, G. (Acarinina) matthewsae, G. (Acarinina) praeaequa, G. (Acarinina) praeangulata,

Globorotalia (Acarinina) praeaequa

Citation: Globorotalia (Acarinina) praeaequa Blow 1979
Rank: species
Type locality: DSDP Site 47 2, core 10, lat. 32 0 26.9' N., long. 1570 42.7' E. holotype (fig. 6) from sect. 4, 83-85 cm; paratype (pl. 81, fig. 7) from sample 10-5, 70-72 cm; two paratypes (pl. 83, figs. 7, 8) from sample 10-3, 78-80 cm; [all in 2689 m water depth on the Shatsky Rise, lat. 320 26.9' N. , long. 157 0 42.7' E. , northeast Pacific Ocean]. Five paratypes (pl. 82, figs. 7-11) from sample DB. 1 76, at the type locality of the Globorotalia uncinata zone of Bolli (1957, U. S. Nat. Mus. Bull. vol. 215, p. 64), Trinidad.
Type age (chronostrat): Lower Paleocene, Danian-Thanetian, Zone P.2 (Globorotalia (Acaranina) praecursoria praecursoria partial-range zone); ranges up to middle Paleocene, Zone P .3 (Globorotalia (Morozovella) angulata angulata partial-range zone) and possibly to lowermost Zone P .4 (Globorotalia (Globorotalia) pseudomenardii partial-range zone).
Type specimens: Holotype: PM PF 63799; Paratype: PM PF 63800
Type repository: London, UK; NHM

Linked specimens: London, UK; NHM (PM PF 63799) London, UK; NHM (63800)

Current identification/main database link:


Original Description
The test is composed of about 1 1½ chambers coiled in a low trochospire and with 4½ chambers in the last convolution of the test. In dorsal aspect, the chambers are much longer tangentially (anterior-posteriorly) than radially broad. The earlier dorsal intercameral sutures are recurved but later become more nearly radial in direction; these sutures are slightly incised but the dorsal surfaces of the last convolution of chambers are not inflated but nearly flat. The equatorial profile is subquadrate and lobulate. In axial-aperture profile, the test is plano-convex with the ventral side appearing like that seen in Globorotalia (Morozovella) aequa aequa Cushman and Renz [Globorotalia crassata (Cushman) var. aequa, Cushman and Renz, 1942]. The peripheral margin is, however, only subacute to acute in the last formed parts of the test but this peripheral margin does not bear a muricocarina; the peripheral margin does have a concentration of muncae but these are not fused or coalesced together. In ventral aspect, the umbilicus is open, fairly broad and not so deep as seen in G. (M.) aequa aequa. The ventral intercameral sutures are broadly but not deeply incised and are subradially disposed. The primary aperture extends from the umbilicus to about one half of the way towards the periphery. The wall surface is distinctly muricate but no pseudolimba- ation or muricocarina is formed.

Size: Maximum diameter of holotype 0.33 mm.

Extra details from original publication
The holotype (fig. 6) shows a larger part of fifth chamber than usually seen in other representatives of the taxon. However, the paratype figured on pl. 81  fig. 7, is similar to the holotype in having a larger part of a fifth chamber and these two specimens were chosen as being a matching pair morphologically.
The paratypes figured on pl. 82, figs. 7-11, illustrate the close relationship between the holotypic morphotype with a larger part of a fifth chamber in the last convolution (cf. pl. 83, fig. 7) to those morphotypes with only 4 chambers visible in the last convolution of the test (cf. pl. 83, fig. 7 and 8 especially). Concomitant with this slight reduction in the number of chambers usually seen in the last whorl, there is a slightly greater degree of peripheral acuteness and ventral vaultation so that with the exception of the peripheral murmcocarina, the test comes to resemble, very closely, that of G. (M.) aequa aequa Cushman and Renz. However, Globorotalia (Acarinina) praeaequa Blow differs from G. (Morozovella) aequa aequa in having a slightly less tightly coiled test, a more distinctly lobulate but less distinctly quadrate equatorial profile, more strongly recurved earlier dorsal intercameral sutures, a less acute peripheral margin and a slightly' wider umbilicus as well as frequently showing (like the holotype of praeaequa) a larger part of the fifth chamber in the final convolution of the test. Most importantly, the main difference between the two taxa lies in the absence of a muricocarina In praeaequa compared to the presence of this structure in aequa (sensu lato).
 The morphotypic variation included for the new taxon G. (A.) praeaequa Blow, 1979, circumscribes a group of non-muricocarmate forms which show transitional features from [the nominate subspecies of] G. (A.) praecursoria (Morozova) [Acuranina praecursoria, 1957] to G. (Morozovella) aequa aequa Cushman and Renz, wherein there is tightening of the coiling-mode combined with a reduction in the number of chambers in the last convolution of the test. In this regard, the specimen figured [by Blow, 1979, op. cit.] on pl. 82, fig. 4, shows transitional characters between praecursoria praecursoria (Morozova) and G. (A.) praeangulata Blow, 1979, inasmuch as this specimen shows the beginning of the anterio-posterior lengthening of the chambers without any significantly tighter coiling-mode. This transitional specimen should be compared to the holotypic form of the new taxon (fig. 6) as well as the paratype shown on pl. 82, fig. 7. A convincing morphogenetic series can be seen by comparing the specimens on pl. 82, figs. 4, 7, 9 and 8 in that order.
 It would seem, that to some extent at least, the trends which operate to produce the G. (Acarinina) praeaequa morphotypes are opposite, but complementary, to the trends which produced the G. (Acarinina) praeangulata morphotypes. These two forms probably should be regarded as the extremes of a plexus of forms which differentiated simultaneously from the praecursoria praecursoria basic stock. In both praeaequa and praeangulata, the earlier chambers retain, in dorsal aspect, the vorticiform appearance of the ancestral praecursoria morphotype with the early dorsal intercameral sutures being quite strongly recurved.
 As can be seen from the specimen figured on pl. 82, fig. 9, small dorsal sutural openings occur in G. (A.) praeaequa Blow, 1979 but these openings are not regarded as functionally true supplementary apertures (see Blow, 1979, op. cit., p. 492). The muricate, but not muricocarinate, periphery of G. (A.) praeaequa Blow, 1979  can be seen from the illustrations given of other paratypes on pl. 83, figs. 7 and 8.

References:

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


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Globorotalia (Acarinina) praeaequa compiled by the pforams@mikrotax project team viewed: 20-10-2020

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