Nannotax3 - ntax_mesozoic - Helicolithus tectufissus

Distinguishing features:
Parent taxon (Helicolithus): Loxolith coccoliths with bicyclic rim with broad inner cycle and narrow central-area, filled by broad cross bars. The rim image is distinctly bicyclic and the inner cycle and cross bars are birefringent.
This taxon: Helicolithus with delicate symmetrical diagonal cross bars divided by median suture.

Citation: Helicolithus tectufissus Blair & Watkins 2009

Synonyms:

Helicolithus stellafissus - this name is used in places in Blair & Watkins (2009) but evidently was changed to H. tectufissus during revision of the manuscript. It was never formally proposed and so is a nomen nudum.

This ellipsoidal coccolith has a bicyclic rim and a thin, diagonal cross. The proximal rim cycle exhibits pronounced birefringence in LM while the distal cycle remains dull. The narrow central area contains a delicate diagonal cross that overlaps the proximal rim and is composed of eight elements. The central area lacks a back plate. Each diagonal arm is composed of two calcite elements. When the major axis aligned north to south in cross- polarized light, visible sutures divide the dextral crossbar. The sinistral crossbar of the diagonal cross will also exhibit a divisional suture when the major axis is 10-30° away from the north-south orientation. This second sutural split is much more subtle. There is no central spine. [Blair & Watkins 2009]
It can be separated from all other Helicolithus and Eiffellithus species by the unique sutural division of the sinistral crossbar of the diagonal cross. This species differs from H. trabeculatus and H. compactus by its delicate diagonal cross and the absence of a back plate. Helicolithus anceps also has a central spine making it easily distinguishable from H. tectufissus. [Blair & Watkins 2009]

4-5.5 µm long (Blair & Watkins 2009)

Geological Range:
Last occurrence (top): within Santonian Stage (83.65-85.70Ma, top in Santonian stage). Data source: Blair & Watkins 2009
First occurrence (base): within Coniacian Stage (85.70-89.39Ma, base in Coniacian stage). Data source: Blair & Watkins 2009

References:

Blair, S. A. & Watkins, D. K. (2009). High-resolution calcareous nannofossil biostratigraphy for the Coniacian/Santonian Stage boundary, Western Interior Basin. Cretaceous Research. 30(2): 367-384. gs

Helicolithus tectufissus

References:

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