Catalog - Globorotalia (Morozovella) spinulosa coronata

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Globorotalia (Morozovella) spinulosa coronata

Citation: Globorotalia (Morozovella) spinulosa coronata Blow 1979

Type locality: Holotype (pl. 168, fig. 8, pl. 230, fig. 5) and nine paratypes (pl. 50, figs. 4, 5; pl. 168, figs. 1-7; pl. 229, figs. 5, 6; pl. 230, fig. 6) from BP Sample RS.24, obtained from trench dug for Kilwa-Masoka water pipe 200 yards west of Kilwa Prison, and one paratype (pl. 50, figs. 2, 3) from BP sample RS.31 1; both in Kilwa, Tanzania. Four additional paratypes (pl. 230, figs. 1-4) from 42 cm, in core KANE 9-C Echo Seamount, north of Cape Verde Islands, central Atlantic Ocean.

Type age (chronostrat): Lower Middle Eocene, lower Lutetian, Zone P. I I (Globigerapsis kugleri/ Subbotinafrontosa boweri concurrent-range zone); ranges from lower Middle Eocene, lowermost Lutetian, Zone P. 10 to Middle Eocene, middle Lutetian, Zone P.13.

Type specimens: Holotype PM PF 64561; Paratype PM PF 64559

Original Description
The moderately large test is coiled in a low trochospire with about 11-12 chambers comprising the spire and with just over 5 chambers visible in the last convolution of the test as seen ventrally. The equatorial profile of the test is lobate and the peripheral margin bears a distinct peripheral test muncocarina. The dorsal intercameral sutures are proximally subradial but become recurved distally and are variably muricate to pseudolimbate. In axial-apertural profile, the test is unequally biconvex with the dorsal side less convex than the quite distinctly vaulted ventral side (cf. the paratype figured on pl. 168, fig. 5). The peripheral margin is acute whilst the primary aperture extends from the umbilicus to about 2/ 3rds of the way to the periphery and is an arched opening with a thickened rim-like apertural margin. In ventral aspect, the umbilicus is widely open with a coronet of muricae surrounding the umbilical depression and borne on the ventral shoulders of the last convolution of chambers (see details of holotype, pl. 230, fig. 5).

Size: Maximum dimensions of holotype 0.43 mm.

Extra details from original publication
The paratypes illustrated on pl. 168, figs. 1-7 and pl. 230, figs. 1-4, together with the paratypic specimens illustrated on pl. 50, figs. 2-5 [see footnote], show the range of variation which the writer associates with his new taxon. The degree of pseudolimbation and the degree to which the muncae are developed over the dorsal intercameral sutures is just as variable in specimens referable to coronata as it is in specimens referable to spinulosa spinulosa Cushman. However, in specimens which show no pseudolimbation, there is always some development of muricae on these sutures and along the length of the spiral suture. In some speci mens of coronata (cf. pl. 230, figs. 1-4), small dorsal openings are present in the spiral suture and even in the more proximal parts of the dorsal intercameral sutures. These openings superficially appear analogous to the true dorsal sutural supplementary apertures of the phylogenetically advanced specimens of Globorotalia (Truncorotaloides) (rohri and topilensis groups) but the author maintains the opinion that, in morozovellid taxa, the openings are due essentially to the 'stand-off* effect noted and discussed in this work (Blow, 1979, op. cit., p. 489). Thus, the writer still considers that these small dorsal openings are due to the gaps originally left between muricae when subsequently calcified test material is formed over previously calcified strongly muricate edges and surfaces.
Details of the primary apertural system of Globorotalia (Morozovella) spinulosa coronata Blow can be observed in the photograph on pl. 230, fig. 6, which shows more highly magnified details of the paratype shown on pl. 168, fig. 5. In this photograph, the thickened apertural rim can be clearly seen.
Essentially, G. (M.) spinulosa coronata differs from G. (M.) spinulosa spinulosa Cushman in possessing a more widely open (not closed) umbilicus which is surrounded by a coronet of muricae borne on the ventral extremities of the umbilical shoulders of the chambers of the last convolution of the test. The coiling-mode of coronata IS more lax than in spinulosa (sensu stricto) and the chambers do not enlarge quite so rapidly as in typical specimens of Cushman's taxon.

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

Pearson, P. N. & Berggren, W. A. (2006). Taxonomy, biostratigraphy, and phylogeny of Morozovelloides n. gen. 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 10): 327-342. gs V O

CATALOG OF ORIGINAL DESCRIPTIONS: Globorotalia (Morozovella) spinulosa coronata Blow 1979

Globorotalia (Morozovella) spinulosa coronata

References:

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