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Prorocentrum arenarium Faust, 1994

Species Overview:

Prorocentrum arenarium is an armoured, marine, sand-dwelling, benthic dinoflagellate species. This toxic species is associated with coral rubble and colored sand in tropical embayments of the Caribbean Sea.

Taxonomic Description:

Prorocentrum arenarium is a bivalvate species often observed in valve view. Cells are round to slightly oval in valve view (Figs. 1,2); cell size ranges between 30 to 32 µm in diameter. Both valves are concave in the center. The thecal surface is smooth (Figs. 1-3) with distinct randomly distributed valve poroids (65-73 per valve). The valve centers are devoid of pores. The poroids vary from kidney-shaped to oblong (Figs. 4,6), with an average size of 0.62 µm long and 0.36 µm wide. Spacing between poroids is 2-3 µm. Valve margins exhibit equally spaced marginal poroids, 50-57 per valve, and are similar in size to valve poroids (Figs. 1-3,6). The valve and marginal poroids are useful diagnostic features of this species and are easily viewed under the light microscope. The intercalary band is smooth and widens during cell division (Figs. 2,3) (Faust, 1994).

The periflagellar area, which lacks ornamentation, is a broad triangle on the right valve at the anterior end of the cell (Figs. 1,4,5). The apical region of the right valve is excavated; the left valve margin is flattened (Fig. 4). The flagellar and auxiliary pores are different sizes (Figs. 4,5). The longitudinal flagellum is short (average length of 11 µm) (Figs. 1,5,9), and both flagella emerge from the flagellar pore (Fig. 5) (Faust, 1994).

Morphology and Structure:

Prorocentrum arenarium is a photosynthetic species with a prominent central pyrenoid (Fig. 10) and a posterior nucleus (Fig. 9). A small (2-3 µm), narrow, tubular, peduncle-like structure in the periflagellar area has been observed in this species (Figs. 7,8). This structure originates and emerges from the flagellar pore, and is adjacent to the longitudinal flagellum (Fig. 7) (Faust, 1994).

Reproduction:

Prorocentrum arenarium reproduces asexually by binary fission.

Species Comparison:

The valve poroids of P. arenarium are distinct from similarly known benthic Prorocentrum species: P. lima has approximately 58-86 round pores per valve and 55-72 marginal pores with a diameter of 0.3-0.7 µm (Faust, 1991); P. maculosum has about 85-90 valve poroids and 65-75 marginal poroids with a diameter of 0.6 µm (Faust, 1993b).

The architecture of the periflagellar area of P. arenarium, with no ornamentation (Faust, 1994), is similar to that of P. concavum, P. ruetzlerianum (Faust, 1990b), P. foraminosum (Faust, 1993b), and P. tropicalis (Faust, 1997).

P. arenarium has a smooth intercalary band. This feature is also characteristic of other benthic Prorocentrum species: P. lima (Faust, 1991), P. hoffmannianum (Faust, 1990), and P. foraminosum (Faust, 1993b).

The peduncle-like organelle in P. arenarium is similar in structure to the peduncle observed in P. norrisianum (Faust, 1997).
Only a few round to nearly round Prorocentrum species are known: P. arenarium (Faust, 1994) is smaller than P. emarginatum (cell diameter 35-40 µm) (Faust, 1990b), but larger than P. ruetzlerianum (cell diameter 28-35 µm) (Faust, 1990b) and P. compressum (cell diameter 36 µm) (Matzenauer, 1933, Böhm, 1936, Schiller, 1937, Tafall, 1942, Dodge, 1975).

Ecology:

Prorocentrum arenarium is a benthic and epiphytic species. Cells are motile, propelled by two flagella, or are attached to sand or coral rubble. This species can be a significant component of benthic Prorocentrum assemblages in colored sand patches in the Caribbean (1200-6000 cells/g sand) (Faust, 1994).

The presence of a peduncle-like structure may indicate mixotrophic feeding within the sand (Faust, 1994).

Toxicity:

This is a known DSP-toxin producing species, producing okadaic acid (OA) (Ten-Hage et al., 2000).

Habitat and Locality:

Prorocentrum arenarium is associated with coral rubble and colored sand in tropical embayments of the Caribbean Sea and the SW Indian Ocean (Faust, 1994, Ten-Hage et al., 2000).

Prorocentrum arenarium