Diversity and distribution of species of the planktonic dinoflagellate genus Alexandrium (Dinophyta) from the tropical and subtropical Mexican Pacific Ocean Author Hernández-Becerril, David U. Author Pichardo-Velarde, Jorge G. Author Alonso-Rodríguez, Rosalba Author Maciel-Baltazar, Ebodio Author Morquecho, Lourdes Author Esqueda-Lara, Karina Author Barón-Campis, Sofía A. Author Quiroz-González, Nataly text Botanica Marina 2023 Warsaw, Poland 2023-11-06 66 6 539 557 http://dx.doi.org/10.1515/bot-2023-0037 journal article 10.1515/bot-2023-0037 1437-4323 11000291 3.1.8 Alexandrium pseudogonyaulax (Biecheler) Horiguchi ex Yuki et Fukuyo ( Figures 38–43 ) References: Balech 1995 , 73, pl. XVI, figs 1–18; Nguyen and Larsen 2004 , 102, pl. 13, figs 1–3; Gu et al. 2013 , 75, figs 4 A–D; Lassus et al. 2016 , 53, pl. 9 A–D; Hernández-Becerril et al. 2021 , 70, 71. Figures 25–27: Alexandrium minutum , LM. (25) Empty cell in ventral view with the first apical plate (1′), ventral pore (arrow) and Po. (26) Outline of a cell. (27) Epitheca with plate tabulation and ventral pore (arrow). Figures 28–37: Alexandrium monilatum , LM and SEM. (28, 29) A long chain (8 cells) and detail of that chain,respectively,LM. (30) Pair of cells in ventral view,SEM.(31) General outline of a cell, LM.(32) Cell in ventral view showing Po and 1′, SEM. (33) Detail of the cingulum and sulcus, showing the first apical plate (1′), SEM. (34) Apical view with plate tabulation, SEM. (35) Hypotheca showing the posterior sulcal plate (Sp) and its connecting pore (arrow), SEM.(36) Po plate with the conjunction pore and foramen, SEM. (37) Posterior sulcal plate showing the connection pore, LM. Figures 38–43: Alexandrium pseudogonyaulax , LM. (38) Cell in ventral view. (39) Empty cell in ventral view, showing 1′, 4′, 6″ and the large ventral pore (arrow). (40) Detail of Po with the foramen. (41–43) Epitheca in ventral view showing 1′, 4′, 6″, and ventral pore (arrow). Solitary cells of medium to relatively large size, ovoid to pentagonal and slightly depressed longitudinally ( Figure 38 ), epitheca slightly domed and shorter than hypotheca ( Figures 38 and 39 ), which has an antapical concavity, cingulum wide and excavated ( Figure 41 ), and sulcus wide and deep ( Figures 38 and 39 ). First apical plate (1′) is not connected to Po ( Figure 39 ) and has a pentagonal shape ( Figures 39, 41 , and 42) and a strong posterior indentation (notch). A large ventral pore appears between this plate and 4′ ( Figures 39, 41–43 ), whereas 6″ is quadrangular. Po is elongate with a classical comma shape ( Figure 40 ). Measurements: 35–42 μm L, 40–45 μm W (Table 1). Toxicity: this species produces goniodomins A and B ( Krock et al. 2018 ). Distribution: in the Gulf of Tehuantepec.