Alexandrium tamiyavanichii Balech

3.1.10 Alexandrium tamiyavanichii Balech (Figures 53–66)

References: Balech 1994, 217, figs 1–6; Balech 1995, 57, pl. XIII, figs 1–19; Usup et al. 2002, 271, figs 6 A–H; Nguyen and Larsen 2004, 106, pl. 15, figs 1–5; Lim et al. 2007, 15, figs 2 A–J; Menezes et al. 2018, 5, figs 2 G–K; Hernández-Becerril et al. 2021, 72, 73.

This species forms medium to large chains with more than 64 cells (Figure 53). Cells are nearly spherical (Figure 53), with non-pronounced shoulders (Figure 54), epitheca and hypotheca about the same proportion (Figure 55), wide and excavated cingulum (Figures 56 and 59), and not prominent apical pore (Figures 62 and 63). Reduced cingular lists and more developed sulcal lists, with their margins reaching until the antapical end, resembling short spines (Figure 59). Plate 1′ is in connection with Po, and is widely rhomboid, with a ventral pore (Figure 58). Po is large, comma-shaped, with a large connecting pore (Figures 62 and 63). The anterior sulcal plate (Sa) is composed by two parts, the most anterior is trapezoid and the posterior similar to others of the genus (Figures 55, 57, 65, and 66), with a conspicuous notch, whereas the posterior sulcal plate (Sp) is irregularly hexagonal and has a large attachment pore with a fine furrow running from its right margin (Figures 60, 61, and 64).

Measurements: 35–42 μm L, 40–45 μm W (Table 1).

Toxicity: this species produces toxins associated to PSP (Xu et al. 2021).

Distribution: in the southern Gulf of California and the central Mexican Pacific.