Pyrodinium bahamense Plate, 1906 var. compressum (Böhm) Steidinger et al., 1980
Species Overview:
P. bahamense var. compressum is an armoured, marine, planktonic dinoflagellate. It is associated with toxic PSP blooms in the tropical and subtropical areas of the Indo-Pacific.
Taxonomic Description:
P. bahamense var. compressum cells are distinctive and are commonly found in chains up to 32 cells long (Fig. 1). Single cells are rounded with a low apical horn at the apex (Fig. 2). Individual cells have distinctive anterior and posterior spines (Figs. 2-4). In intact chains only the anterior cell has an apical spine, and only the most posterior cell has an antapical spine. Cells in chains show distinct anterio-posterior compression (Fig. 1). The strongly developed thecal surface is covered with fine dense spinulae and large, prominent pores (Figs. 2-4). Anterior and posterior attachment pores are present (Fig. 5). Strong low ridges mark the edge of most sutures, some ridges are more developed than others (Figs. 1-6). Cell size ranges: 33-47 µm in length, 37-52 µm in transdiameter, and 37-47 µm in dorso-ventral diameter (Steidinger et al., 1980, Balech, 1985a, Taylor and Fukuyo, 1989, Taylor et al., 1995).
Thecal Plate Description:
The plate formula for P. bahamense var. compressum is: (Po, cp), 4', 6'', 6C, 8S, 6''', 2''''. On the epitheca a low apical horn is present, and to its right, a small apical spine (Fig. 2). Two antapical spines are present on the hypotheca (Figs. 2-4) (Steidinger et al., 1980, Balech, 1985a, Taylor and Fukuyo, 1989, Taylor et al., 1995).
The triangular apical pore complex (APC) (Figs. 4,5) 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 (=anterior attachment pore) (AP) along its right margin (Fig. 5). The first apical plate (1') approaches, but does not come in contact with the APC (Fig. 4). Plate 1' has two long anterior-lateral sides, tapering anteriorly to a somewhat rounded or obliquely truncated end (Balech, 1985a, Taylor and Fukuyo, 1989).
The cingulum, with six plates, bears pores along the upper and lower margin (Fig. 2). It has strong cingular lists, is displaced about 1 time its width, and is left-handed (Figs. 1-4). The sulcus, with eight plates, is rather shallow with well developed sulcal lists (Figs. 3,4,6). The lists are large and contact each other anteriorly. Strong left antapical spines support a well-defined posterior sulcal list (Figs. 3,4). The posterior sulcal plate is narrow, with a slit-like posterior attachment pore (Steidinger et al., 1980, Balech, 1985a, Taylor and Fukuyo, 1989, Taylor et al., 1995).
Morphology and Structure:
P. bahamense var. compressum is a photosynthetic species with golden chloroplasts, a large anterior vacuole, and a centrally located oblong nucleus (Buchanan, 1968).
Reproduction:
P. bahamense var. compressum reproduces asexually by binary fission.
Species Comparison:
Distinguishing features of Pyrodinium are the apical spines and the strongly developed sutural ridges. P. bahamense var. compressum can be confused with Triadinium (= Goniodoma) polyedricum which also has ridges along its sutures. However, T. polyedricum is more angular in shape, never occurs in chains, and lacks the antapical spines of P. bahamense var. compressum. The APC of P. bahamense var. compressum is composed of two platelets, Po and cp, whereas in T. polyedricum the plates are fused to produce one plate, Po (Taylor and Fukuyo, 1989).
Cell tabulation in P. bahamense var. compressum is nearly identical to some Alexandrium species (e.g. A. minutum, A. monilatum and A. pseudogonyaulax). But P. bahamense var. compressum 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. Some species of Alexandrium form long chains of cells similar in appearance to that of P. bahamense var. compressum. However, the cells in the Alexandrium chains are round, not polygonal as in P. bahamense var. compressum (Taylor and Fukuyo, 1989).
Some species of Gonyaulax may also be confused with P. bahamense var. compressum, but these occur singly, lack ridges and plates, and have a greater girdle displacement (Taylor and Fukuyo, 1989). Also, the resting cyst of P. bahamense var. compressum is very different from any known in Gonyaulax (Wall and Dale, 1968; Wall and Dale, 1969).
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 was 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 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 neurotoxins 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.