Rhagodiscus


Classification: Mesozoic -> Eiffellithales -> Rhagodiscaceae -> Rhagodiscus
Sister taxa: Calcicalathina, Percivalia, Rhagodiscus, Zebrashapka,

Distinguishing features: Loxolith coccoliths with low rim and central-area filled by a granular plate which may be perforate and/or spine-bearing. In xpl the rim is unicyclic moderately bright, the central area is granular, lacking a clear extinction cross.


Daughter taxa: (blue => in age window 0-800Ma)
species with large, prominent, process
Small (4-6µm) Rhagodiscus with relatively narrow central area spanned by a granular plate bearing large spine/spine base. The rim image is distinctly dark in XPL.
Large (>8.0 µm) loxolith coccoliths with a wide central area (usually greater than twice as wide as the rim) that is spanned by a granular plate. A relatively large spine or spine base is typically present. The rim and plate usually show yellow interference colors in XPL.
Elongate, narrow Rhagodiscus with parallel or slightly concave sides and a spine/spine base that spans the central area.
Medium-sized (5-8µm) murolith coccoliths with a relatively broad central area spanned by a granular plate that normally bears a hollow spine or spine base; the rim appears unicyclic in LM.
Small (~4µm) loxolith coccoliths with granular basal plate and 'cross-bars' supporting a large, flaring spine with serrated edges. In LM, this species may be virtually indistinguishable from small specimens of R. asper.
Small Rhagodiscus with a birefringent spine/spine base that almost fills the central area.
Large with central hollow spine between two large circular pores with raised, birefringent edges.
Small-medium, sub-rectangular with parallel sides, rounded ends and a narrow central area spanned by a large hollow spine base. The rim may be irregularly thickened. Often seen in side view.
Large Rhagodiscus coccoliths with a very broad spine-base that is distinctly striated in LM XPL.
species with process present but not prominent
Medium-sized unicyclic loxolith coccoliths with a wide central area spanned by a butterfly-shaped bar with raised, birefringent edges.
Small (<5µm), elliptical Rhagodiscus with a length/width ratio of <2.5, straight or slightly convex longer sides, and a central area filled with a granular plate which supports a hollow spine base.
Medium to large elliptical rhagodiscid-like coccolith with moderately broad rim and narrow central area spanned by a spine (base). Rim is unicyclic in XPL and overall the coccolith exhibits low birefringence.
Small (holotype 4 µm), with small slender spine with bright tip
Medium-sized with a complex axial-cross
Large (>8.0 µm) loxolith coccoliths with a broad rim (usually as broad or broader than the central area) and a central area spanned by a granular plate; a relatively large spine or spine base is usually present. The broad and blocky rim shows yellow interference colors under XPL.
Large, central area relatively broad and spanned by, raised, bridge-like structure.
species lacking a process
Medium sized, with wide rim and no spine, weakly asymmetric
A species of Rhagodiscus with construction and light microscopic image similar to that of R. achlyostaurion, but which is larger (length c. 6.5-8.5 µm, width c. 5.0-6.5 µm), with a relatively narrower rim and broad central area, with no spine or a small spine base.
Reniform Rhagodiscus with an irregularly thickened rim.
Specimens not identified to species level

Taxonomy:

Citation: Rhagodiscus Reinhardt, 1967
Rank: Genus
Type species: Rhagodiscus asper (Stradner, 1963) Reinhardt, 1967.
Synonyms:

Farinacci & Howe catalog pages: Rhagodiscus * , Alfordia * , Viminites * , Mitosia + * , Rhabdolithina *

Distinguishing features: Loxolith coccoliths with low rim and central-area filled by a granular plate which may be perforate and/or spine-bearing. In xpl the rim is unicyclic moderately bright, the central area is granular, lacking a clear extinction cross.

Search data:
TagsLITHS: murolith, elliptical, quadrate, CA: cross-axial, plate, pores, process, R-UNITS: R-prominent, DETAILS: rim-unicyclic,
MetricsLith size: 4->12µm;
Sources: 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): near top of Tithonian Stage (87% up, 145.9Ma, in Tithonian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Black, M. (1975). British Lower Cretaceous Coccoliths. I-Gault Clay (Part 3). Palaeontographical Society Monograph. 128: 113-142. gs :: ::

Bown, P. R., Rutledge, D. C., Crux, J. A. & Gallagher, L. T. (1998). Early Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 86-131. gs :: ::

Reinhardt, P. (1967). Fossile Coccolithen mit rhagoidem Zentralfeld (Fam. Ahmuellerellaceae, Subord. Coccolithineae). Neues Jahrbuch für Geologie und Paläontologie Monatshefte. 1967: 163-178. gs :: ::

Worsley, T. R. (1971). Calcareous nannofossil zonation of Upper Jurassic and Lower Cretaceous sediments from the Western Atlantic. In, Farinacci, A. (ed.) Proceedings of the Second Planktonic Conference Roma 1970. Edizioni Tecnoscienza, Rome 2: 1301-1321. gs :: ::


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Rhagodiscus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 16-7-2020

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=11012 Go to Archive.is to create a permanent copy of this page - citation notes



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