Protoperidinium leonis (Pavillard) Balech 1974 . Rev. Mus. Argent. Cienc. Nat. “ B. Rivadavia ”, Hydrobiologia 4 (1): 60. (Figs. 44–46) .

References: Lebour 1925: 112, Pl. XXI, Fig. 1 a–d; Schiller 1937: 236, Fig. 236 a–m; Kiselew 1950: 196, Figs. 333 a–b, 334 a–d; Wood 1954: 104, Fig. 148 a–c (as Peridinium leonis); Abé 1981: 384, Fig. 58 (398–404); Steidinger & Tangen 1997: 540, Pl. 51; Krakhmalnyi 2011: 200, Table 83, 1–10; Phan-Tan et al. 2016: 526, Fig. 5 a–e.

Basionym: Peridinium leonis Pavillard 1916 . Inst. Botan. Univ. Montpell. St. Zoolog. Cette, Travail. Ser. mixte. Mem. 4: 32, Fig. 6.

Description: Cells rhomboid in ventral and dorsal views, with straight sides. The apical pore structure of Aʹ– type (Toriumi & Dodge 1993). The epithecal plate pattern comprises seven precingular plates (7ʹʹ), four apical plates (4ʹ), three anterior intercalary plates (3a), 1ʹ plate – “ortho”, 2a – “hexa”. The precingular plates with undulating longitudinal ribs and pores. The cingulum median, descending (displaced by about 1.0 cingular width). The sulcus deep and oblique. The hypotheca tapers into two low conical antapical horns ending in strong spines. Dimensions: 52–95 μm long and 53–95 μm wide.

Nomenclatural note: The species could be easily confused with P. obtusum Karsten and P. conicum . However, it can be distinguished from P. obtusum by its asymmetrical 1ʹ plate and strongly oblique cingulum (Phan-Tan et al. 2016). Protoperidinium conicum differs from P. leonis by a wider 1ʹ.

Distribution: Coastal and oceanic, in temperate to tropical waters; cosmopolitan (Steidinger & Tangen 1997). Data on the distribution of P. leonis are given from the GBIF.org (2022) (Fig. 89).