Classification: Coccolithophores -> Nannolith families inc sed -> Rhomboasteraceae -> Tribrachiatus
Sister taxa: Rhomboaster, Tribrachiatus,

Daughter taxa: (blue => in age window 0-800Ma)
Tri-radiate forms with long ray tip bifurcations that deviate strongly from the plane of the nannolith, giving the appearance of two asymmetrically offset and superimposed tri-radiate cycles.
Single cycle tri-radiate forms with long ray tip bifurcations (around 25% or more of the total arm length). The rays are in the same plane and the bifurcations only slightly deviate from that plane.
Large, single-cycle tri-radiate nannoliths with little or no ray end bifurcation (<25% of the total arm length).
one arm <½ length of the other two, the others slightly curved, tips bent and pointed.
one arm reduced to short knob, the others curved giving recent-shape, tips pointed.
Specimens which cannot be assigned to any established species


Citation: Tribrachiatus Shamrai, 1963
Rank: Genus
Type species: Tribrachiatus orthostylus Shamrai, 1963.

Distinguishing features: Solid nannoliths with three rays that typically have terminal bifurcations.

Farinacci & Howe catalog pages: Tribrachiatus

Search data:
TagsLITHS: nannolith-radiate, N: 3D-radiate, star-shaped,
CSPH: not known, V-UNITS: all, R-UNITS: none, DETAILS: 1ou,
MetricsLith size: 8->20µm; Segments: 3->3;
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): in upper part of Ypresian Stage (67% up, 50.5Ma, in Ypresian stage). Data source: Total of range of species in this database
First occurrence (base): in lower part of Ypresian Stage (15% up, 54.7Ma, in Ypresian stage). Data source: Total of range of species in this database

Plot of occurrence data:


Perch-Nielsen, K. (1985a). Cenozoic calcareous nannofossils. In, Bolli, H. M. , Saunders, J. B. & Perch-Nielsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge 427-555. gs

Shamrai, I. A. (1963). Nekotorye formy verkhnemelovykh i paleogenovykh kokkolitov i disko_asterov na yuge russkol platformy [Certain forms of Upper Cretaceous and Paleogene coccoliths and discoasters from the southern Russian Platform]. Izv. Vyssh. Ucheb. Zaved. Geol. i Razv. 6(4): 27-40. gs


Tribrachiatus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 18-11-2019

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Short stable page link: Go to to create a permanent copy of this page - citation notes

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