Protoperidinium excentricum (Paulsen) Balech 1974 . Revta Mus. Argent. Cienc. Nat. “ B. Rivadavia ”, Hydrobiologia 4 (1): 54. (Figs. 6, 8–9) .

References: Paulsen 1908: 51, Fig. 64; Lebour 1925: 108, Pl. XVIII, Fig. 1 a–d; Schiller 1937: 144, Fig. 145 a–g; Kiselew 1950: 160, Figs. 254 a–g, 261 a–g; Wood 1968: 102, Fig. 299 (as Peridinium excentricum); Dodge 1982: 174, Fig. 19 j, k; Dodge 1985: 53; Okolodkov 2008: 107, Pl. 5–7; Krakhmalnyi 2011: 197, Table 81, 5–6.

Basionym: Peridinium excentricum Paulsen 1907 . Medd. Komm. Hav. Kbhvn., Ser. Plankton 1 (5): 14, Fig. 17.

Description: Cells discoid, asymmetrical, strongly anteroposteriorly compressed. The apical horn shifted towards the left side. The apical pore structure of Bʹ– type (Toriumi & Dodge 1993). The epithecal plate pattern comprises seven precingular plates (7ʹʹ), four apical plates (4ʹ), two anterior intercalary plates (2a), 1ʹ plate – “ortho”, 2a – “hexa”. The cingulum median, excavated. The sulcus reaches the antapex, bears lists. The cytoplasm pink. Dimensions: 25–48 μm long and 37–64.3 μm wide.

Distribution: Temperate to tropical waters; cosmopolitan (Steidinger & Tangen 1997). Data on the distribution of P. excentricum are given from the GBIF.org (2022) (Fig. 86).