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Votadinium rhomboideum

From Fensome et al., 2019:
Votadinium rhomboideum Gurdebeke, Mertens, Pospelova, Matsuoka, Li Zhen and Louwye in Gurdebeke et al., 2019b, VRp.16, pl.6, figs.1–14.
Holotype: Gurdebeke et al., 2019b, pl.6, figs.1–8.
Motile equivalent: Protoperidinium quadrioblongum, according to Gurdebeke et al. (2019b, VRp.16).
Age: Holocene.

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Original description: [Gurdebeke et al., 2019b]:

Votadinium rhomboideum sp. nov.
Gurdebeke, Mertens, Pospelova, Matsuoka, Li & Louwye
Plate 6, figures 1–14

Synonymy.
1983 Cyst of Protoperidinium oblongum: Dale, figs 11–12.
1987 Protoperidinium oblongum: Baldwin, fig. 14.
2000 Cyst of Protoperidinium oblongum (Aurivillius) Parke & Dodge: Della Tommasa et al., pl. 1, fig. 7.
2000 Protoperidinium oblongum type b: Rubino et al., fig. 2r.
2001 Cyst of Protoperidinium oblongum: Dale, figs 1–7, 8.
2004 Cyst of Protoperidinium oblongum: Joyce, p. 178, fig. 18.
2004 ‘Pre-excysted protoperidinioid cyst’: Kawamura, fig. 15.
2004 Cyst of Protoperidinium oblongum: Morquecho & Lechuga-Deveze, fig. 12.
2004 Cyst of Protoperidinium oblongum, Orlova et al., fig. 58.
2006 Cyst of Protoperidinium oblongum: Fujii & Matsuoka, fig. 4-e.
2008 Cyst of Protoperidinium oblongum: Ribeiro & Amorim, pl. 2, fig. b.
2008 Votadinium calvum: Vilanova et al., pl. 1, fig. J.
2010 Votadinium calvum: Pospelova et al., pl. 6, fig. 3.
2010 Votadinium calvum: Uzar et al., fig. 25.
2011 Votadinium carvum [sic.]: Aydin et al., fig. 27.
2011 Votadinium calvum: Pasuram et al., pl. 1, fig. 8.
2011 Votadinium calvum: Price & Pospelova, pl. 4, fig. 4.
2013 Cyst of Protoperidinium oblongum, Orlova & Morozova, fig. 4f, g.
2013 Cyst of Protoperidinium quadrioblongum: Sarai et al., pl. 3, figs 1–4.

Motile stage equivalent. Protoperidinium quadrioblongum Sarai et al., 2013, according to Sarai et al. (2013).
Holotype. Patricia Bay, Saanich Inlet (48°39.005'N, 123°29.027'W; station PB 3 in Mertens et al. 2012), surface sediments, UVic 2012-197-1 (EF R20/4, label to the right), Plate 6, figures 1–8.

Repository. Royal Belgian Institute of Natural Sciences (RBISN, Brussels), accession no. IRSNB b7157.

Diagnosis. Brownish cysts, rhomboidal in outline in ventral or dorsal view, length and width comparable. Epi- and hypocyst sides are straight or slightly concave, giving the cyst an angular outline. Cyst wall smooth. Two rounded antapical horns rounded and generally symmetrical, sometimes right horn slightly broader. Sulcal area incised and carrying flagellar scar. Antapical concavity deeply incised and U-shaped. Archeopyle (type IA, 2a) large, trapezoidal, saphopylic and involving the apex.

Description. Rhomboidal/pentagonal cyst with straight outlines. Cyst width and length comparable, with L/W = 0.98 (0.87–1.05, N = 4), although the length is obscured when the apex is lost with archeopyle. Cyst is smooth and has a single wall.

Dimensions. Sarai et al. (2013): length 61 (70) 84 µm, width 59 (67) 80 µm, L/W 0.88–1.05 (N = 4). Own measurements:
Holotype: length 65.4 µm, width 62.2 µm; range: length 65.4–73.1 µm, width 62.2–69.5 µm, L/W 0.95 (N = 2).

Remarks. Votadinium rhomboideum is not identical to the cyst of Protoperidinium oblongum (Aurivillius) Paulsen reported by Wall and Dale (1968, pl. 1, fig. 29), as was suggested by Sarai et al. (2013).

Comparison. Votadinium rhomboideum sp. nov. differs from V. calvum and V. spinosum in that it has a higher L/W ratio and straight outlines for the epi- and hypocyst. It lacks ornamentation, which distinguishes it from V. spinosum and V. pontifossatum, and it differs from V. pontifossatum and V. reidii in having the apex involved in the operculum. It can be distinguished from V. nanhaiense and V. elongatum by the
position of the archeopyle and general outline. Finally, V. concavum has concave outlines of the epi- and hypocyst, rather than straight edges.

Distribution and stratigraphic range. The species was observed here in the South China Sea and Saanich Inlet. Based on the synonymy list, Votadinium rhomboideum occurs globally, but with most reports from the North Atlantic and North Pacific domains.
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