Pyrodinium bahamense Plate, 1906 var. bahamense
Species Overview:
P. bahamense var. bahamense is an armoured, marine, bioluminescent dinoflagellate associated with non-toxic blooms in tropical and subtropical waters of the Atlantic.
Taxonomic Description:
P. bahamense var. bahamense is a very distinctive species. Cells are almost round, roughly polyhedral, with a strongly developed theca and pronounced apical and antapical spines (Fig. 1). Distinctive and prominent ridges arise from most sutures (Figs. 1-3,6,7). Never more than 2 cells together. Relatively large trichocyst pores with thickened rims (Figs. 1-3,6,7), as well as numerous fine teeth-like pustules (on mature cells) (Figs. 4,5), are present on the thecal surface. Young cells have very thin, smooth porate plates. Cell size varies: 33-71 µm in length and 33-67 µm in transdiameter (Wall and Dale, 1969, Steidinger et al., 1980, Balech, 1985a, Taylor and Fukuyo, 1989, Taylor et al., 1995).
Thecal Plate Description:
The plate formula for P. bahamense var. bahamense is: (Po, cp), 4', 6'', 6C, 8S, 6''', 2''''. On the epitheca a high apical horn is present (Figs. 1,6), and to its right, a winged apical spine (Figs. 1-5). Two prominent antapical spines are present on the hypotheca: one longer than the other (Figs. 1-3). The triangular apical pore complex (APC), located on the apical horn, is made up of two plates: the apical pore plate (Po) is a narrow outer plate with large pores; and the closing plate (cp) is a leaf-shaped inner plate with a narrow, oblong apical pore (AP) on its margin (Figs. 4,5). The first apical plate (1') approaches, but does not come in contact with the APC (Fig. 1). Plate 1' has two long anterior-lateral sides, tapering anteriorly to a somewhat rounded or obliquely truncated end (Steidinger et al., 1980, Balech, 1985a, Taylor and Fukuyo, 1989, Taylor et al., 1995).
The cingulum, with six plates, bears pores along the upper and lower margins (Figs. 2,3,6,7). It has strong cingular lists, is displaced about 1 time its width, and is left handed (Figs. 1-3,7). The sulcus, with eight plates, is rather shallow with well developed sulcal lists (Figs. 1,3). The lists are large and contact each other anteriorly. Strong left antapical spines support a well-defined posterior sulcal list (Fig. 1) (Steidinger et al., 1980, Balech, 1985a, Taylor and Fukuyo, 1989, Taylor et al., 1995).
Morphology and Structure:
P. bahamense var. bahamense is a photosynthetic species with golden chloroplasts, a large anterior vacuole, and a centrally located oblong nucleus (Buchanan, 1968).
Reproduction:
P. bahamense var. bahamense reproduces asexually by binary fission.
Species Comparison:
P. bahamense var. bahamense can be confused with Triadinium polyedricum which also has ridges along its sutures. However, Triadinium is more angular in shape and lacks the prominent spines of Pyrodinium. Moreover, the APC of Pyrodinium is composed of two platelets, Po and cp, whereas in Triadinium they are fused into one plate, Po (Taylor and Fukuyo, 1989).
Cell tabulation in Pyrodinium is nearly identical to some Alexandrium species (e.g. A. minutum, A. monilatum and A. pseudogonyaulax). But Pyrodinium cells have a much heavier theca with strong surface markings, sutural ridges and a polygonal shape. Alexandrium spp. have spherical shapes with rounded profiles. Their thecal plates are thin, smooth and delicate (Taylor and Fukuyo, 1989).
Some species of Gonyaulax may also be confused with Pyrodinium, but these lack sutural ridges and have a greater girdle displacement. Distinguishing features of Pyrodinium are the apical spines and the strongly developed sutural ridges. Also, the resting cyst of P. bahamense is very different from any known in Gonyaulax (Wall and Dale, 1968, Wall and Dale, 1969, Taylor and Fukuyo, 1989, Taylor et al., 1995).
Varietal Comparisons:
Steidinger et al., 1980 compared thecate cells of tropical Atlantic and Indo-Pacific P. bahamense and recognized several minor morphological and physiological differences, enough to warrant variety status. Hence, the taxonomy of the species was revised and two varieties were established: var. bahamense for the Atlantic population and var. compressum for the Indo-Pacific population. However, Balech, 1985a reported morphological variation within both populations, and states that P. bahamense cannot be divided into any infraspecific taxa (Taylor and Fukuyo, 1989). Balech (1985a) states that the species is highly variable (Fig. 7) and that the toxicity of the Indo-Pacific populations is most likely induced by external factors.
Established differences between the two varieties: a.) var. bahamense has a prominent apical horn and a well developed winged apical spine, whereas var. compressum has a shorter, less pronouned apical horn that is broader at the base, usually lacks a prominent apical spine, and is anterio-posterorly compressed; b.) var. bahamense may occur in pairs but does not form chains, while var. compressum is most often found in chains of 2-32 cells; c.) var. bahamense generally has smaller thecal pores and more prominent thecal spines with wide bases than var. compressum which has pustules between trichocyst pores; and d.) var. bahamense is bioluminescent and non-toxic, while var. compressum is not bioluminescent and produces a neurotoxin that causes PSP (Steidinger et al., 1980, Taylor and Fukuyo, 1989, Steidinger and Tangen, 1996). Because both varieties share a number of common characteristics, a few single cells of the var. compressum would be difficult to recognize as distinct (Steidinger et al., 1980).
Matsuoka et al., 1985 reported that the resting cyst of the Indo-Pacific variety was similar morphologically to the Atlantic variety (both cysts spiny) except for cyst diameter and length of surface processes (Taylor and Fukuyo, 1989).
Remarks:
Balech, 1985a states that the anterior-posterior compression of the body and the presence or absence of an apical spine are not reliable systematic characteristics to warrant varietal status in P. bahamense. He found many variations within the tropical Atlantic specimens.