Protoperidinium euxinum Krachmalny 2023, sp. nov.
Creators: name: Krakhmalnyi, Maxim
name: Krakhmalnyi, Aleksandr
name: Terenko, Galyna
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Chromista
Myzozoa
Dinophyceae
Peridiniales
Protoperidiniaceae
Protoperidinium
Protoperidinium euxinum

description: Protoperidinium euxinum Krachmalny sp. nov.   
(Fig. 2, A–E)  
 Division Dinoflagellata (Butschli 1885) Fensome et al. 1993.   
 Class Dinophyceae Pascher 1914.   
 Order Peridiniales Haeckel 1894.   
 Family Protoperidiniaceae Balech 1988 nom. cons.   
 Genus Protoperidinium Bergh 1881.   
 Diagnosis:— Cells medium-sized (length 88.6±7.2 µm, min. 73.3 µm, max. 99.0 µm; width 45.4±4.0 µm, min. 38.8 µm, max. 51,6 µm; n=20), pentagonal, elongated, slightly compressed dorsoventrally. Epitheca conical, with straight or concave lateral sides, tapers into a narrow and relatively long apical horn. Epitheca larger than the hypotheca, “meta–penta” type. The plate 2a asymmetrical, laterally compressed. Cingulum ascending by about one-half of its height, shallow and bears lists. Hypotheca inverse trapeziform, with large slightly divergent antapical horns bearing wide membranes. Sulcus straight, broad, shallow, slightly invades the epitheca, reaches the antapex. The sulcal area bordered. Thecal surface with fine reticulations and numerous pores. Cells colorless or light brown. Nucleus spherical, located in the center of the epitheca.   
 Holotype:— Fig. 2, A–Е. The specimen on which the illustration is based was collected in the northwestern part of the Black Sea (Odessa Bay) in August 2020, at 46°26′28.25′′N, 30°46′25.52′′E (Fig. 1: MF, Maliy Fontan).   
 Etymology:— The specific epithet was chosen in order to emphasize the locality of this species—the Black Sea, which was called in ancient times “Pontus Euxinus”.   
 Paratype:— The phytoplankton sample was preserved in 4% formaldehyde solution and is stored at the Institute for Evolutionary Ecology of the National Academy of Sciences of Ukraine (Kiev, Ukraine).   
 Ecology and distribution:— Protoperidinium euxinum reaches large numbers in Odessa Bay (northwestern part of the Black Sea, sampling sites are shown in Fig. 1) during the warm period of the year. Water temperature and salinity were 20° C and 18 psu, respectively. Occurs together with Protoperidinium steinii (Jørgensen) Balech and P. mediterraneum (Kofoid) Balech.   
 Description:— Cells of Protoperidinium euxinum are medium-sized (73.3–99.0 µm in length and 38.8–51.6 µm in width), shaped like elongated pentagons (Fig. 2, A–B; Fig. 3, A; Fig. 4, A, B, K), slightly compressed dorsoventrally (Fig. 4, B, E, F, J). The epitheca is conical, with straight or slightly concave lateral sides (Fig. 2, C, D; Fig. 3, B, C; Fig. 4, A–K), tapers into a narrow and relatively long apical horn (Fig. 2, A, B). The apical pore plate (Po) connects with the plate 1’ through a small and narrow plate “x” (Fig. 2, A). The epitheca is larger than the hypotheca, the plate arrangement is “meta–penta”; plates 1’ and 2a are pentagonal (Fig. 2, A, E; Fig. 3, B, D, E; Fig. 4, D, H). The plate 1a is also pentagonal (Fig. 4, G). The plate 2a is asymmetrical, laterally compressed, the length of the suture between plates 1a and 2a is greater than between 3’ and 2a (Fig. 2, E; Fig. 3, E; Fig. 4, H). The plate 3a is hexagonal (Fig. 4, I). The cingulum is ascending by about one-half of its height, shallow, composed of plates C1–C3 and transitional plate “t”, and bears lists with pronounced ribs (Fig. 2, A, B; Fig. 3, B, C; Fig. 4, A). The sulcal area is bordered by lists (Fig. 3, F, G). The sulcus is straight, broad, shallow, slightly invades the epitheca (plate Sa), reaches the antapex, composed of the plates Sa, Sd, Ss, Sm and Sp. The right sulcal plate (Sd), in its apical part, tapers into a very narrow protrusion that overlaps the cingulum and reaches 7’’. The left side of Sd has a well-developed fin (Fn). The plate Ss is covered by the left sulcal list (Ll), which is attached to the plates 1’’’ and 1’’’’ and merges with the left antapical horn. The small median sulcal plate (Sm) and partially the posterior sulcal plate (Sp) are positioned under the fin of the plate Sd (Fig. 2, A; Fig. 3, F; Fig. 4, A). The right sulcal list is underdeveloped. The hypotheca is inverse trapeziform, with large slightly divergent antapical horns bearing membranes; the right horn is more tilted to the side (Fig. 2, A, B; Fig. 3, A, G; Fig. 4, A, K, L). Thecal surface with fine reticulations and numerous pores (Fig. 3, B–E). Cells are colorless or light brown. The nucleus is spherical, located in the center of the epitheca (Fig. 3, H).
description: Published as part of Krakhmalnyi, Maxim, Krakhmalnyi, Aleksandr & Terenko, Galyna, 2023, Protoperidinium Euxinum (Protoperidiniaceae, Dinophyceae) - A Novel Dinoflagellate Species From The Plankton Of The Black Sea, pp. 229-236 in Phytotaxa 598 (3) on pages 231-232, DOI: 10.11646/phytotaxa.598.3.4, http://zenodo.org/record/7969964