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Brigantedinium cariacoense

Brigantedinium cariacoense, (Wall, 1967), Lentin and Williams, 1993

Originally Chytroeisphaeridia, subsequently (and now) Brigantedinium. Harland, 1981, and Lewis et al., 1984, considered this species to represent the encysted stage of Protoperidinium avellana (Meunier, 1919) Balech, 1974. This combination was not validly published in Reid, 1977, since the generic name Brigantedinium was not validly published at that time.

Holotype: Wall, 1967, pl.16, fig.14
Locus typicus: Core A420/18, depth 380cm.,10¦ 30.8" N., 64¦ 40" W, Caribbean
Stratum typicum: Quaternary

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Original description as Chytroeisphaeridia cariacoensis: [Wall, 1967, p. 113-114]:

Diagnosis:
A spherical dinoflagellate cyst with a large elongate hexagonal dorsal intercalary archeopyle.

Description:
The test is spherical, often with sharp secondary folds bordering depressions, and penetrated by a hexagonal dorsal, intercalary archeopyle. This is elongated equatorially, its width being almost equal to twice its height, while its size (around 16 x 28 µm) and shape are constant.
Other splits occur in the test but do not reflect a tabulation.
The wall is thin and may enclose.
An inner capsule with either a minutely thin, hyaline wall or a waxy yellow refractive wall. There are often small, granular inclusions within the cell lumen. Unmacerated cysts are characteristically brown but they become paler after oxidation.

Affinities:
Chytroeisphaeridia simplicia Wall 1965 differs by having an asymmetrical, hexagonal archeopyle with a length: breadth ratio of 1:1. The natural affinities of both species lie with Peridinium, and the archeopyle represents the loss of a dorsal intercalary plate.
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