Alexandrium pseudogonyaulax (Biecheler) Horiguchi ex Yuki and Fukuyo, 1992
Species Overview:
Alexandrium pseudogonyaulax is an armoured, marine, planktonic dinoflagellate. It is a toxic species found in coastal regions and brackish environments.
Taxonomical Description:
Cells of A. pseudogonyaulax are medium to large, irregularly pentagonal-shaped with moderate dorsoventral flattening. Cells are wider than long; the epitheca is slightly shorter than the hypotheca (Figs. 1,2). The first apical plate (1') is characteristically displaced with a large ventral pore on the anterior margin (Figs. 3,4). The thecal plates are smooth and thin with scattered minute pores. Cells range in size between 34-60 µm in length and 39-69 µm in width (Balech, 1995, Montresor et al., 1993, Steidinger and Tangen, 1996).
Thecal Plate Description:
The plate formula for A. pseudogonyaulax is: Po, 4', 6'', 6c, 10s, 5''', 2''''. The apical pore plate (Po) is oval shaped, contains a large comma-shaped foramen and a number of irregular pores, and is positioned longitudinally on the apex (Figs. 3,4,9). The distintive 1' plate does not come in contact with the Po; it is roughly pentagonal and wider anteriorly (Figs. 3,4,9). The sloped anterior margin bears a large ventral pore that is wider than long (Figs. 3,4). The ventral pore does not penetrate the 4' plate (Figs. 3,4) (Balech, 1995, Montresor et al., 1993, Yuki and Fukuyo, 1992).
The short, convex epitheca is dome-shaped (Figs. 1,2). The hypotheca is slightly longer with an obliquely concave antapex (Figs. 1,2). The shallow cingulum is displaced in a descending fashion less than one time its width (Figs. 1,8). The sulcus lacks lateral lists. It slightly penetrates the epitheca obliquely on the right (Balech, 1995).
Morphology and Structure:
A. pseudogonyaulax is a photosynthetic species with central radiating yellow-brown chloroplasts. The transversely elongated nucleus is large and curved, and centrally located (Balech, 1995, Montresor, 1995).
Reproduction:
A. pseudogonyaulax reproduces asexually by binary fission. This species also has a sexual cycle with isogamous mating types. The smaller rounder gametes (Fig. 5) fuse (one gamete engulfs the other), produce a planozygote which then encysts into a characteristic resting cyst (Figs. 6,7) (Montresor et al., 1993, Montresor, 1995).
Ecology:
A. pseudogonyaulax is a coastal and brackish water dinoflagellate species. Blooms of this species are commonly reported in the Strait of Georgia, British Columbia (North Pacific Ocean) (Taylor and Haigh, 1993).
This species produces a characteristic and unusual resting cyst: a non-smooth cyst. The cysts are round and dark, and are often covered with a mucilaginous layer (Fig. 6). They contain a reddish-orange accumulation body. Size ranges from 40 to 55 µm in diameter. The cyst wall consists of two layers: a smooth inner layer and a paratabular outer layer (Fig. 7). The cyst paratabulation equals the tabulation of a vegetative cell. This is the only reported species in the genus Alexandrium to produce a non-smooth cyst (Montresor et al., 1993, Nichetto et al., 1995).
Species Comparisons:
A. pseudogonyaulax closely resembles two other Alexandrium species: A. hiranoi and A. satoanum. Common features include general shape and size, and lack of contact of the first apical plate, 1', with the Po. Distinguishing features lie in the cell outline, the ventral pore, the 1' plate, cyst morphology and habitat: a) A. hiranoi has a round shape, A. pseudogonyaulax is wider than long, A. satoanum is also wider than long with the general outline resembling a top: the epitheca and hypotheca have straighter sides; b) the ventral pore of A. hiranoi is circular and invades the 4' plate, in A. pseudogonyaulax the ventral pore is semi-circular and does not invade the 4', and in A. satoanum, no ventral pore is present (has a.a.p. and p.a.p); c) the 1' plate in A. hiranoi is slender and rectangular, whereas in A. pseudogonyaulax the 1' is almost pentagonal; d) the cyst of A. hiranoi is smooth, while the cyst of A. pseudogonaulax is paratabulate with thick sutures; and e) A. hiranoi is found in rockpools, A. pseudogonyaulax is found in coastal brackish habitats (Kita and Fukuyo, 1988, Montresor et al., 1993, Steidinger and Tangen, 1996).
This species roughly resembles A. tamarense; however, the latter species is not as round, and has a broader APC (Taylor et al., 1995).