Prorocentrum mexicanum Tafall, 1942
Species Overview:
Prorocentrum mexicanum is an armoured, marine, benthic dinoflagellate species. This toxic species is commonly found in tropical shallow embayments.
Taxonomic Description:
Prorocentrum mexicanum is a bivalvate species often observed in valve view. Cells are ovate to oblong with straight sides (30-38 µm long and 20-25 µm wide) (Figs. 1,2). The valve surface of young cells is smooth (Figs. 4-6), but in older cells it may appear rugose (Figs. 1-3). Both valves have many large trichocyst pores (100 per valve) radially arranged in furrowed depressions (Figs. 1-4), and 80 marginal pores (Fig. 7) (Faust, 1990). Trichocyst pores are round with a smooth edge (0.5 µm in diameter) and even in size (Figs. 5,6). Cells with ejected trichocysts are common. The center of the cell is devoid of pores. The intercalary band is broad and transversely striated (Figs. 2,3) (Faust, 1990b).
The periflagellar area, located apically and off-center on the right valve, is a relatively small, V-shaped, shallow depression (Fig. 1). It houses a prominent curved periflagellar collar adjacent to the auxiliary pore. Opposite is a smaller periflagellar plate adjacent to the flagellar pore (Fig. 3). The curved periflagellar collar is large (2 X 6 µm) and may appear as an apical spine, and has been reported as such (Fukuyo, 1981, Carlson, 1984). Both valves are escavated (Faust, 1990b).
Morphology and Structure:
P. mexicanum is a photosynthetic species with a posterior nucleus (Faust, 1990b).
Reproduction:
Prorocentrum mexicanum reproduces asexually by binary fission. Sexual reproduction has also been observed in natural cell populations (M.A. Faust, pers. com.).
Species Comparisons:
With its prominent periflagellar collar, P. mexicanum most resembles P. caribbaeum in general cell shape; however, P. caribbaeum is a larger species, is broader and heart-shaped, and broadest in the anterior region (Dodge, 1975, Faust, 1993a).
Trichocyst pore morphology is also similar in these two species; however, significant differences lie in the number of trichocyst pores: P. caribbaeum has a greater number of pores per valve (145-203) than P. mexicanum (100 per valve). Ejected trichocysts are often observed in cells of both species (Faust, 1990b, Faust, 1993a).
P. mexicanum, P. emarginatum and P. caribbaeum all have radially arranged valve pores and display two different sized pores (Loeblich et al., 1979b, Fukuyo, 1981, Steidinger, 1983, Faust, 1990b, Faust, 1993a).
The periflagellar area and platelet architecture of P. caribbaeum is similar to that of P. mexicanum (Carlson, 1984, Faust, 1993a).
The intercalary band of P. mexicanum is transversely striated. This is similar to P. caribbaeum and P. emarginatum (Faust, 1990b, Faust, 1993a).