Helicolithus


Classification: ntax_mesozoic -> Eiffellithales -> Eiffellithaceae -> Helicolithus
Sister taxa: Eiffellithus, Helicolithus, Tegumentum

Distinguishing features: 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. 


Daughter taxa (time control age-window is: 0-800Ma)
diagonal cross
Helicolithus anceps
Medium-sized (6-8µm) Helicolithus with symmetrical diagonal cross bars.
Helicolithus trabeculatus
Clearly bicyclic Helicolithus with symmetrical diagonal cross bars
Helicolithus leckiei
Small (3-4µm), strongly bicyclic, margin between cycles scalloped; birefringent diagonal cross; cross-bars straight and simply constructed.
Helicolithus tectufissus
Helicolithus with delicate symmetrical diagonal cross bars divided by median suture.
(sub)axial cross
Helicolithus turonicus
Large (>6µm) Helicolithus with axial cross bars. Longitudinal bar longer than transverse bar.
Helicolithus varolii
Helicolithus with axial cross bars. Cross bars similar in length, and longitudinal bar does not reach ends of central area.
Helicolithus compactus
Helicolithus with cross bars rotated slightly from the axial position.
Helicolithus blairiae
A small to medium-sized; axial cross nearly fills central area; sinuous-shaped longitudinal bar separates two very short, disjunct segments along the short axis.
Helicolithus sp.
Specimens not identified to species level

Taxonomy:

Citation: Helicolithus Noël, 1970
Rank: Genus
Type species: Discolithus anceps Górka, 1957

Farinacci & Howe catalog pages: Helicolithus *

Distinguishing features: 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. 


Morphology: Most species do not seem to have processes - but the type species, H. anceps, is an exception to this.
Cross-bars are typically prominent and divided longitudinally.

Search data:
TagsLITHS: murolith, elliptical, CA: cross-axial, ca_disjunct, diagonal cross, closed, CROSS-POLARS: rim-bicyclic, V-prominent, R-prominent,
MetricsLith size: 3->8µm;
Data source notes: size range of included species
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): at top of Maastrichtian Stage (100% up, 66Ma, in Maastrichtian stage). Data source: Total of range of species in this database
First occurrence (base): in lower part of Aptian Stage (18% up, 123.9Ma, in Aptian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Burnett, J. A. (1998). Upper Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 132-199. gs V O

Górka, H. (1957). Les Coccolithophoridés du Maestrichtien supérieur de Pologne. Acta Palaeontologica Polonica. 2: 239-284. gs V O

Noël, D. (1970). Coccolithes Crétacés: La Craie Campanienne du Bassin de Paris. Éditions du Centre National de la Recherche Scientifique, Paris. -. gs


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Helicolithus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 1-3-2021

Taxon Search:
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Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=10505 Go to Archive.is to create a permanent copy of this page - citation notes



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