Rhagodiscus

Distinguishing features:
Parent taxon (Rhagodiscaceae): Eiffelithales with V-units forming most of rim (R-units typically thin plates on proximal surface, so LM images are typically unicyclic. Central-areas typically filled by a plate of granular calcite. The central structure may be spine-bearing, perforate or massive.
This taxon: 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 (time control age-window is: 0-800Ma)
				species with large, prominent, process
				Rhagodiscus achlyostaurion 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.
				Rhagodiscus amplus 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.
				Rhagodiscus angustus Elongate, narrow Rhagodiscus with parallel or slightly concave sides and a spine/spine base that spans the central area.
				Rhagodiscus asper 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.
				Rhagodiscus cepekii 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.
				Rhagodiscus dekaenelii Small Rhagodiscus with a birefringent spine/spine base that almost fills the central area.
				Rhagodiscus infinitus Large with central hollow spine between two large circular pores with raised, birefringent edges.
				Rhagodiscus pseudoangustus 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.
				Rhagodiscus splendens Large Rhagodiscus coccoliths with a very broad spine-base that is distinctly striated in LM XPL.
				species with process present but not prominent
				Rhagodiscus adinfinitus Medium-sized unicyclic loxolith coccoliths with a wide central area spanned by a butterfly-shaped bar with raised, birefringent edges.
				Rhagodiscus gallagheri 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.
				Rhagodiscus indistinctus 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.
				Rhagodiscus pancostii Small (holotype 4 µm), with small slender spine with bright tip
				Rhagodiscus plebeius Medium-sized with a complex axial-cross
				Rhagodiscus robustus 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.
				Rhagodiscus sageri Large, central area relatively broad and spanned by, raised, bridge-like structure.
				Rhagodiscus sicutclipeus Small to medium-sized (4.5–6 μm) normally elliptical; central area relatively wide with a small spine base, which is bright in XPL. The coccolith is distinctly dark in XPL.
				species lacking a process
				Rhagodiscus eboracensis Medium sized, with wide rim and no spine, weakly asymmetric
				Rhagodiscus hamptonii 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.
				Rhagodiscus reniformis Reniform Rhagodiscus with an irregularly thickened rim.
				Rhagodiscus sp. Specimens not identified to species level

Taxonomy:

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

Distinguishing features:
Parent taxon (Rhagodiscaceae): Eiffelithales with V-units forming most of rim (R-units typically thin plates on proximal surface, so LM images are typically unicyclic. Central-areas typically filled by a plate of granular calcite. The central structure may be spine-bearing, perforate or massive.
This taxon: 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.

Geological Range:
Last occurrence (top): at top of Late Maastrichtian Substage (100% up, 66Ma, in Danian stage). Data source: Total of ranges of the species in this database
First occurrence (base): within NJT17a subzone (143.55-143.97Ma, base in Tithonian stage). Data source: Total of ranges of species in this database

Plot of occurrence data:

• Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
• Triangles indicate an event for which a precise placement has been suggested
• Neptune data: This is a higher taxon page so Neptune data is not plotted. See also: customisable plot Parent: Rhagodiscaceae

Rhagodiscus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 16-10-2024 Taxon Search: Advanced Search Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=11012 Go to Archive.is to create a permanent copy of this page - citation notes