Protoperidinium pellucidum Bergh 1881 . Vidensk. Medd. naturh. Foren i Kbhvn.: 227, Figs. 46–48. (Figs. 47–52).

References: Paulsen 1908: 49, Fig. 61; Schiller 1937: 212, Fig. 209; Kiselew 1950: 190, Fig. 316 a–d (as Peridinium pellucidum); Wood 1968: 106, Fig. 320; Okolodkov 2008: 113, Pl. 4, Fig. 4–7; Krakhmalnyi 2011: 204, Table 86, 3–15; Al-Yamani & Saburova 2019: 318, Pl. 177.

Synonyms: Peridinium pellucidum (Bergh) Schütt 1895 .

Description: Cells broadly pyriform, slightly dorsoventrally compressed. The epitheca dome-shaped, with a short apical horn. The apical pore structure of Bʹ– type (Toriumi & Dodge 1993). The epithecal plate pattern comprises seven precingular plates (7ʹʹ), four apical plates (4ʹ), three anterior intercalary plates (3a), 1ʹ plate – “para”, 2a – “hexa”. The cingulum median, ascending (displaced by 0.5–1.0 cingular width), bordered. The sulcus straight, broadens towards the antapex, bears lists. The hypotheca almost hemispherical, with two short antapical spines, and two sulcal lists continuations between the spines. The plate 1ʹʹʹ bears hypothecal pore (Dodge 1987; Okolodkov 2003). The cytoplasm colorless to pale pink. Dimensions: 30.0–68.0 μm long and 30.0–70.0 μm wide.

Distribution: Mainly coastal and cosmopolitan in temperate to tropical waters (Steidinger & Tangen 1997). Data on the distribution of P. pellucidum are given from the GBIF.org (2022) (Fig. 92).