Alexandrium catenella (Whedon and Kofoid) Balech, 1985b
Species Overview:
Alexandrium catenella is an armoured, marine, planktonic dinoflagellate. It is associated with toxic PSP blooms in cold water coastal regions.
Taxonomical Description:
A chain-forming species, A. catenella typically occurs in characteristic short chains of 2, 4 or 8 cells (Figs. 1,5). Single cells are round, slightly wider than long, and are anterio-posteriorly compressed (Figs. 1,5,8). A small to medium sized species, it has a rounded apex and a slightly concave antapex (Figs. 1,5,8). The thecal plates are thin and sparsely porulated. Cells range in size between 20-48 µm in length and 18-32 µm in width (Fukuyo, 1985, Fukuyo et al., 1985, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).
Thecal Plate Description:
The plate formula for A. catenella is: Po, 4', 6'', 6c, 8s, 5''', 2''''. The epitheca and hypotheca are nearly equal in height. The hypotheca bears prominent sulcal lists that resemble spines (Fig. 1). In chain forms, anterior attachment pores (aap) and posterior attachment pores (pap) are present (Fig. 2) (Fukuyo, 1985, Fukuyo et al., 1985, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).
The apical pore complex (APC) is broad, triangular and widens dorsally (Figs. 2,3,9). The apical pore plate (Po) houses the characteristic fishhook shaped foramen, and, if catenate, an ellipsoidal anterior attachment pore (aap) (Figs. 2,9). There are two diagnostic features of this species: a.) the first apical plate, 1', comes in contact with the Po; and b.) a ventral pore (vp) is absent (Figs. 2-4,9). The median cingulum is lipped, deeply concave, and is displaced in a descending fashion one time its width (Figs. 1,8). The sulcus is deeply impressed and widens posteriorly (Figs. 1,8). The wide posterior sulcal plate houses the pap near the right margin (Fukuyo, 1985, Fukuyo et al., 1985, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).
Morphology and Structure:
A. catenella is a photosynthetic species with numerous yellow-green to orange-brown chloroplasts. The nucleus is large and U-shaped (Whedon and Kofoid, 1936).
Reproduction:
A. catenella reproduces asexually by binary fission. This species also has a sexual cycle with opposite mating types (heterothallism). After gamete fusion, a planozygote forms which then encysts into a characteristic resting cyst (Figs. 6,7) (Yoshimatsu, 1981).
Species Comparisons:
A. catenella is very similar morphologically (size, shape and thecal plate formula) to A. tamarense. Differences lie in the shape of the Po, and presence or absence of a vp. The Po in the former species is slightly smaller, and the vp is absent (Figs. 2,3) (Fukuyo, 1985). Molecular testing conducted on A. catenella from Japan and A. tamarense from Japan and the U.S.A. revealed a close genetic relationship between the two species, however they remain distinct (Adachi et al., 1995).
Chains of this species are quite distinctive, but can resemble A. tamiyavanichi; however, A. tamiyavanichi is a warm water species and can be distinguished from A. catenella by its conical shape (Taylor et al., 1995).