Nannoconus funiculus


Classification: Mesozoic -> Braarudosphaerales -> Nannoconaceae -> Nannoconus -> Nannoconus - atypical -> Nannoconus funiculus
Sister taxa: N. funiculus, N. ligius, N. magnadiscus, N. nicholasii, N. pseudoseptentrionalis, N. sabinae,


Taxonomy:

Citation: Nannoconus funiculus Lees & Bown 2016
Rank: Species
Notes & discussion:

The new species is somewhat dissimilar to other nannoconids, being very narrow, elongated and with a double-helix-like arrangement of elements of variable shape; however, other species have ‘scalloped’ outer morphologies (e.g. N. abundans) and there are enough shared characteristics for funiculus to be reasonably included in Nannoconus.

Farinacci & Howe catalog pages: Nannoconus funiculus *


Morphology remarks: SEM - elongate, narrow, tapering nannoconid with a relatively narrow central canal, formed from a double-helix-like arrangement of elements that are loosely arranged at the base, giving an ornate appearance to the lower part, and more tightly arranged at the apex, producing a smooth, parallel-sided, rope-like structure. The basal plate/cycle of this species is composed of a single? cycle of more-or-less horizontal-lying, subtriangular elements, the outer edges of which are rounded and which appear to slightly imbricate. Above this is a cycle of widely-spaced, radial, elongate, subrhomboidal? elements that sit on, or are fused with, the basal (subtriangular elements) cycle. In the cycles above, it is not clear whether the structure is composed of rhomboidal elements or a combination of these with the type of elements shown  Nannoconus nicholasii, which are subtriangular, with the outer edge being scalloped, so as to produce a rounded point and two depressions along that edge, giving a trilobed appearance. In Pl.3, fig.17, the elements of a section through an ornate part of the nannoconid are clearly rhomboidal, and this is also more or less so (subrectangular/subrhomboidal) in a section through the smooth, apical part in Pl.3, figs 11 and 16, the difference being the orientation of the elements. However, side-views of the alignment of elements in the ornate part of the nannoconid suggest that they are composed of the scalloped-triangular elements (Pl.3, figs 12–14), and it is thus possible that the ornate-rhomboid part (Pl.3, fig.17) is an apical portion of this nannoconid, transitioning into the rectangle/rhomb-structured, single-rope, apical feature. So, until we have more information, the ornate, helical portion of this nannoconid is produced by either one point of a narrow rhomb or the scalloped edge of a triangular element pointing outwards. These elements are arranged at an angle, stacked in layers of around six per helix, and imbricate. The double-helix effect is produced by the points of the rhombs/scalloped edge of one strand being offset by one point from the other strand, giving the appearance of two ropes spiralling upwards together (Pl.3, fig.15). The apical portion of this nannoconid appears to be composed of subrectangular/subrhomboidal elements, but here they are arranged with a straight edge outwards, so as to produce a smooth, parallel-sided appearance (Pl.3, figs 10, 11, 16). The double-helix effect is less noticable in this portion because of this, with the two strands being distinguished only by a striped effect in the SEM. This apical portion can vary dramatically in length, and appears to terminate in a knob, although most of our specimens are broken. Consequently, it is not possible to give a definitive length for the holotype.  [Lees & Bown 2016]

LM - N. funicu­lus is distinctively highly birefringent, even when rotated, with a relatively very narrow, tapering outline and narrow canal, and with an angled-striped appearance, due to the distinctive double-helix arrangement of the elements  [Lees & Bown 2016]

Size: L = 8.0μm (but note that the length of the apical ‘rope’ structure is highly variable: Pl.3, g.10 L = 14.3μm), W = 3.0μm at widest, 0.6μm at narrowest. [Lees & Bown 2016]

Search data:
TagsLITHS: nannolith-radiate, circular, cylindrical, hollow, CA: vacant, T-UNITS: T-prominent,
MetricsLith size: 5->10µm;
Sources: illustrated specimens
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): within UC8 zone (91.78-92.99Ma, top in Turonian stage). Data source: Lees & Bown 2016
First occurrence (base): within UC6b subzone (93.55-93.73Ma, base in Turonian stage). Data source: Lees & Bown 2016

Plot of occurrence data:

  • (NB There is no histogram as there are no occurrence records for the taxon in the Neptune database) Parent: Nannoconus - atypical

    References:

    Lees, J. A. & Bown, P. R. (2016). New and intriguing calcareous nannofossils from the Turonian (Upper Cretaceous) of Tanzania. Journal of Nannoplankton Research. 36(1): 83-95. gs


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    Nannoconus funiculus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 23-2-2020

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    Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=10748 Go to Archive.is to create a permanent copy of this page - citation notes



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