Alexandrium acatenella (Whedon & Kofoid) Balech 1985

A. acatenellais a planktonic species associated associated with paralytic shellfish poisoning (PSP) events and red tides. Populations are most abundant in neritic waters at 15ºC. A bloom event in British Columbia caused four human illnesses and one death in 1965, the first reported PSP outbreak associated with A. acatenella. Cell densities during this red tide were as high as 13.5 X 106 cells/L (Whedon & Kofoid 1936; Prakash & Taylor 1966).

A. acatenella is widely distributed in Pacific coastal waters. Populations have been recorded from the north Pacific coast of the United States and Canada, Japan, Argentina and northern Chile (Whedon & Kofoid 1936; Balech 1995; Taylor et al. 1995; Steidinger & Tangen 1996).

A. acatenella is a photosynthetic species with elongated chloroplasts. Cells can be highly pigmented and reddish-brown in color. The elliptical nucleus is C-shaped and equatorial (Whedon & Kofoid 1936; Prakash & Taylor 1966; Balech 1995).

Holotype: Gonyaulax acatenella Whedon and Kofoid, 1936: 31, 33-34, figs. 8-13
Type Locality: NW Pacific Ocean: San Diego, California, USA

A. acatenella reproduces asexually by binary fission (Whedon & Kofoid 1936).

A. acatenella is very similar morphologically (size, shape and thecal plate formula) to the toxic Atlantic species, A. tamarense. Differences lie in the general shape of the cell, thecal sculpture, length of epitheca in relation to the hypotheca, and size and shape of the apical plates. The former species is roundish, while the latter is wider (shoulders) and roughly pentagonal. Thecal plates in A. acatenella are clearly porolated, while in A. tamarense they are relatively smooth. The epitheca in A. acatenella is distinctly longer than the hypotheca; they are nearly equal in A. tamarense. The size and shape of the apical plates differ in these two species (Balech 1995). A. acatenella also shares some common characteristics of A. catenella. However, the former species is a non-chain former without a posterior attachment pore, bears a ventral pore on 1', and is usually found in warmer waters (Prakash & Taylor 1966; Balech 1995).

Alexandrium acatenella is an armoured, marine, planktonic dinoflagellate. It is associated with toxic PSP blooms in Pacific coastal regions.

Gonyaulax acatenella Whedon and Kofoid, 1936
Protogonyaulax acatenella (Whedon and Kofoid) Taylor, 1979

A non-chain forming species, cells of A. acatenella are small to medium sized, longer than wide, and angular to round in ventral outline (Figs. 1, 2). A characteristic ventral pore is present (Fig. 3). Two short antapical spines are present; no apical horn (Fig. 3). The thecal surface is sculptured with large and small pores. Cells range in size between 35-51 µm in length and 26-35 µm in transdiameter width (Whedon & Kofoid 1936; Balech 1995; Taylor et al. 1995; Steidinger & Tangen 1996).

The plate formula for A. acatenella is: Po, 4', 6'', 6c, 9s, 5''', 2''''. The epitheca in this species is longer than the hypotheca: often it is equal to the length of the hypotheca plus the cingulum. The cone-shaped epitheca is low with convex sides (Figs. 1-3). The apical pore complex (APC) is roughly rectangular. The apical pore plate (Po) is broadly oval and narrows ventrally; it bears a relatively large and comma-shaped foramen (Fig. 4). The first apical plate (1') comes in direct contact with the Po, and also bears the characteristic ventral pore (vp) (Fig. 4) (Whedon & Kofoid 1936; Balech 1995; Taylor et al. 1995; Steidinger & Tangen 1996). The post-median cingulum is deeply excavated, and displaced in a descending fashion about 1 time its width without overhanging. Narrow lists are present on the cingulum (Figs. 1-3). The deeply excavated sulcus widens posteriorly flaring to the right, slightly invading the hypotheca. The short hypotheca is broadly rounded with two posterior antapical spines (Figs. 1-3). The antapex region between the spines is slightly concave (Whedon & Kofoid 1936; Balech 1995; Taylor et al. 1995; Steidinger & Tangen 1996).

Alexandrium acatenella is a known PSP toxin-producing dinoflagellate species responsible for several illnesses and one death in British Columbia (Prakash & Taylor 1966).