Alexandrium tamarense (Lebour) Balech

Hernández-Becerril, David U., Pichardo-Velarde, Jorge G., Alonso-Rodríguez, Rosalba, Maciel-Baltazar, Ebodio, Morquecho, Lourdes, Esqueda-Lara, Karina, Barón-Campis, Sofía A. & Quiroz-González, Nataly, 2023, Diversity and distribution of species of the planktonic dinoflagellate genus Alexandrium (Dinophyta) from the tropical and subtropical Mexican Pacific Ocean, Botanica Marina (Warsaw, Poland) 66 (6), pp. 539-557 : 547

3.1.9 Alexandrium tamarense (Lebour) Balech ( Figures 44–52 )

References: Hallegraeff et al. 1991, 582, figs 33–42; Balech 1995, 38, pl. VI, figs 1–40, pl. VII, figs 1–9; Usup et al. 2002, 270, figs 5 A–E; Nguyen and Larsen 2004, 104, pl. 14, figs 1–5; Gu et al. 2013, 75, figs 4 E–I; Fabro et al. 2017, p. 1210, figs 1 A–M.

Cells usually solitary, but cells in couples were also found. Cells relatively small, irregularly pentagonal in shape, with the epitheca slightly larger than the hypotheca ( Figure 44 ), with not pronounced shoulders ( Figure 45 ), wide and excavated cingulum ( Figure 46 ), and central nucleus ( Figure 44 ). The first apical plate (1′) is connected with Po ( Figures 45, 47, 50–52 ), widely rhomboid in shape ( Figures 45 and 51 ), with a ventral pore ( Figures 50–52 ), whereas 2′, 3′ and 4′ are larger plates ( Figure 51 ), and plate 6″ is relatively small and pentagonal ( Figures 46 and 50 ). Po is elongate, more rectangular and comma-shaped, with no pore ( Figures 50–52 ). The posterior sulcal plate (Sp) is wide and pentagonal, with a conspicuous pore ( Figures 48 and 49 ).

Measurements: 26–35 μm L, 28–36 μm W (Table 1).

Toxicity: this species may produce toxins associated to PSP ( Lugliè et al. 2017).

Distribution: in the southern Mexican Pacific, including the Gulf of Tehuantepec.

Remarks: All morphological characters examined led us to identify this species as A. tamarense . However, the fact that species of the “ A. tamarense complex” cannot be distinguished based on morphology alone and that molecular assays are required for reliable identification ( Litaker et al. 2018), puts us in a difficult situation, and it is recommended to consider Alexandrium pacificum Litaker as the prevalent species of that complex in the Pacific Ocean. See Discussion.

Figures

Figures 44–52: Alexandrium tamarense, LM and SEM. (44) Cell in ventral view, LM. (45) Empty cell in ventral view with plate tabulation, LM. (46) Detail of the epitheca with some plates and ventral pore (arrow), LM. (47) Apical view, with plate tabulation, LM. (48, 49) Hypotheca with plate tabulation, including the posterior sulcal plate (Sp) and its pore (arrow), LM. (50) Epitheca with plate tabulation and the ventral pore (arrow), SEM. (51) Epitheca with plate tabulation, SEM. (52) Po with some plates surrounding it, and the ventral pore (arrow), SEM.