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Alexandrium tamiyavanichi Balech, 1994

Species Overview:

Alexandrium tamiyavanichi is an armoured, marine, planktonic dinoflagellate. It is a producer of strong PSP toxins in the Gulf of Thailand.

Taxonomical Description:

A chain-forming species, A. tamiyavanichi typically occurs in chains of 8 cells or more. Single cells are small and round to slightly wider than long (Figs. 1,2). A small ventral pore, vp, is present on the apical 1' plate (Figs. 3-5). The thecal plates are thin and strongly porulated. Cells range in size between 31-41 µm in length and 26-35 µm in transdiameter width (Balech, 1995, Fukuyo et al., 1989, Taylor et al., 1995).

Thecal Plate Description:

The plate formula for A. tamiyavanichi is: Po, 4', 6'', 6c, 10s, 5''', 2''''. The broad apical pore complex (APC) is triangular and narrows ventrally (Figs. 3,5). The apical pore plate (Po) is wide and oval with a large comma-shaped foramen (Figs. 3,5). Several small pores are present along the margin of the Po (Fig. 5). The anterior attachment pore (aap) is large, round and adjacent to the Po (Fig. 5). The first apical plate (1') is large and wide with straight sides, and is in direct contact with the Po (Figs. 3-5). A small ventral pore is present on the anterior right margin of this plate (Figs. 3-5) (Balech, 1967, Balech, 1995, Fukuyo et al., 1989, Taylor et al., 1995).

The conical epitheca is wider than long with shoulders (Figs. 1,2). The hypotheca is slightly longer than the epitheca (Figs. 1,2). The deeply excavated cingulum is displaced in a descending fashion one time its width (Figs. 2,4). The sulcus is deep and widens posteriorly (Figs. 2,4). The sulcus invades the epitheca via the distinctive anterior sulcal plate (s.a.); this plate is divided into two parts by a transverse rib. It is the anterior extension of the s.a. plate (either triangular or rectangular in shape) which projects into a notch in the epitheca (Figs. 2,4,5). Two wing-like sulcal lists project toward the antapex (Fig. 4). The round posterior attachment pore, pap, is present in the center of the posterior sulcal plate (Balech, 1967, Balech, 1995, Fukuyo et al., 1989, Taylor et al., 1995).

Morphology and Structure:

A. tamiyavanichi is a photosynthetic species. The transversely elongated nucleus is lunate shaped (Balech, 1995).


A. tamiyavanichi reproduces asexually by binary fission.

Species Comparisons:

A. tamiyavanichi is often and easily misidentified as A. cohorticula: cell size and outline is similar, both with an anterior extention of the s.a. plate, and both species are chain formers. However, there are number of substantial morphological differences between these two species: In A. cohorticula, the epitheca is longer than wide; the Po is longer; the first apical plate, 1', is thinner; the pap is larger and oval shaped; and the sulcal lists are larger and projected behind the hypotheca (Balech, 1995).
Chains of A. tamiyavanichi can resemble A. catenella. The epitheca in A. tamiyavanichi, however, is conical in comparison to the rounded epitheca of A. catenella (Taylor et al., 1995).


A. tamiyavanichi is a coastal planktonic species (Balech, 1994).


A. tamiyavanichi produces potent PSP toxins similar to those produced by A. tamarense: gonyautoxins, GTX, and saxitoxin, SXT (Fukuyo et al., 1989, Kodama et al., 1988). This species has been the main causative organism of PSP in Thailand waters (Kodama et al., 1988).

Habitat and Locality:

A. tamiyavanichi is a coastal species that has only been reported from three warm-water localities: Gulf of Thailand (type locality), Manila Bay in the Philippines, and from the Andaman Sea, southwest of Thailand (Balech, 1995).

Alexandrium tamiyavanichi