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Trinovantedinium pallidifulvum

Trinovantedinium pallidifulvum Matsuoka, 1987, p.63–64, pl.13, figs.1–9.

Holotype: Matsuoka, 1987, pl.13, figs.7–9.
Age: Holocene.

Original description (Matsuoka, 1987):
Trinovantedinium pallidifulvum sp. nov. Plate 13, figures 1-9
Derivation of name : Latin pallidus+fulvus, lightly brownish ; with reference to the lightly brownish-pigmented cyst wall.

Diagnosis : Intermediate pentagonal cysts slightly brownish-pigmented, consisting of thin autophragm, and covered with very short and apparently nontabular spines. Epicyst large conical with a small apical horn and straight outline in dorso-ventral view, and hypocyst trapezoidal in dorsoventral view, relatively small, and bearing two small antapical horns. Paracmgulum represented by two parallel rows of spines and shallow indentation of wall, avoiding spines and hardly displaced at the ventral area. Parasulcus indicated by shallow indentation without spine and widening toward the antapex. Archeopyle intercalary, basically hexagonal, steno delta-form and formed by the loss of the 2a paraplate.

Holotype: Slide no. AK2-2 (87.4/27.6) ; PL 13, figs. 7-9; Sample no. AK2, Recent sediment in Akkeshi Bay, Hokkaido, North Japan.
Description : The epicyst is always larger than the hypocyst. The cyst wall thickened at the apex and antapex. Two antapical horns are sometimes lacking. The paratabulation is represented by no feature. Two small depressions which probably represent the flagellar pores are sometimes present in the parasulcus.
Dimensions : Cyst length 52.2-70.8 µm, width 56.0-63.4 µm, width of paracingulum 4.9-6.3 µm, length of processes ca. 2.5 µm (Holotype ; cyst length 58.0 µm, width 56.0 µm, width of paracingulum ca. 6 µm). Number of specimens observed : 12.

Remarks : This species resembles Trinovantedinium capitatwn in possessing a pentagonal body covered with many short spines, but differes from the latter in bearing a slightly brownish-pigmented cyst wall and in that the epicyst is always larger than the hypocyst.
Equivalent thecate form : Unknown, but probably a species assignable to the Conica group of the Protoperidinium, based on its browmsh-pigmented cyst wall and intercalary archeopyle.
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