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Prorocentrum norrisianum Faust, 1997

Species Overview:

Prorocentrum norrisianum is an armoured, marine, benthic dinoflagellate species. This species is associated with floating detritus and coral rubble in tropical embayments of the Caribbean Sea .

Taxonomic Description:

Prorocentrum norrisianum is a bivalvate species often observed in valve view. Cells are small and ovate with straight sides (Figs. 1,2). Cells are 20-25 µm in length and 13-16 µm in width. The thecal surface is smooth and delicate with small surface pores (Figs. 1-6). Two different pore sizes are present: minute pores (< 0.05 µm in diameter) and larger pores (0.1 µm in diameter) (Figs. 2,3). Pores are uniformly round with a smooth edge. Approximately 95 to 105 large pores per valve are present, arranged in a distinct pattern (Figs. 2,3). Smaller pores are located only in the apical area along the intercalary band (Fig. 3). The valve center is devoid of pores. The intercalary band is smooth and widens during cell division (Figs. 1,2) (Faust, 1997).

The periflagellar area is a small, shallow, V-shaped depression located off-center on the right valve. It is composed of eight apical platelets without ornamentation (Figs. 1,4). The flagellar and auxiliary pores are unequal in size (Figs. 4,5). Both flagella emerge from the flagellar pore (Fig. 5). The left valve anterior margin is inclined and slightly depressed (Figs. 2,3) (Faust, 1997).

Morphology and Structure:

Prorocentrum norrisianum is a photosynthetic species containing golden-brown chloroplasts. The pyrenoid is centrally located with a nucleus situated posteriorly (Fig. 7) (Faust, 1997).

Scanning electron microscopy reveals a short, tubular, peduncle-like structure in the periflagellar area (Fig. 6). This structure, about 1.6 µm long, emerges from the flagellar pore (Faust, 1997).

Reproduction:

P. norrisianum reproduces asexually by binary fission.

Species Comparison:

The oval shape and size (20-25 µm long and 13-16 µm wide) of P. norrisianum distinguishes this species from other small Prorocentrum species: P. ovum is round (13 µm diameter) (Dodge, 1975); P. arenarium is nearly round (30-32 µm diameter) (Faust, 1994); P. nanum is oval-shaped (8-10 µm long and 6.5-12 µm wide), as is P. cassubicum (22-25 µm long and 16 µm wide) (Dodge, 1975); and P. elegans is oblong (15-20 µm long and 10-14 µm wide) (Faust, 1993a).

The valve pore pattern of P. norrisianum differs from other small Prorocentrum species in pattern and number/valve: a.) pores are in an array pattern in P. elegans, 20-22 pores/valve (Faust, 1993a); as well as in P. formosum, 42-55 pores/valve (Faust, 1993b); and in P. triestinum, 7 pores/valve (Dodge, 1975); b.) pores are in a radiated arrangement in P. venetum, 35-40 pores/valve (Tolomio and Cavolo, 1985a); and c.) pores are irregularly scattered in P. ovum, 10-14 pores/valve (Dodge, 1975); and similarly in P. nanum, 6 pores/valve (Dodge, 1975).

Only a few ovate species with straight sides are known in the genus Prorocentrum. P. norrisianum is larger than P. elegans (15-20 µm long and 10-14 µm wide) (Faust, 1993a), whereas it is smaller than P. formosum (25-28 µm long and 15-16 µm wide) (Faust, 1993b) and P. mexicanum (30-38 µm long and 20-25 µm wide) (Faust, 1990b).

A smooth intercalary band is characteristic of other benthic Prorocentrum species: P. reticulatum (Faust, 1997), P. lima (Faust, 1991), P. hoffmannianum (Faust, 1990b), P. foraminosum (Faust, 1993b), P. arenarium, P. sabulosum and P. sculptile (Faust, 1994), and P. belizeanum (Faust, 1993a).

The periflagellar pore pattern in this species is similar to P. arenarium (Faust, 1994) and P. lima (Faust, 1991).

The peduncle-like structure present in P. norrisianum is morphologically similar to the one observed in P. arenarium (Faust, 1994).

Ecology:

Prorocentrum norrisianum is a benthic and epiphytic species. Cells are motile or are attached to detritus or coral rubble. This species is a minor component of dinoflagellate assemblages. The presence of a peduncle-like structure in this species indicates possible mixotrophy within floating detritus communities (Jacobson and Anderson, 1986, Elbrachter, 1991, Faust, 1994, Faust, 1997).

Toxicity:

The toxicity of this species is unknown.

Habitat and Locality:

Populations of P. norrisianum are often associated with floating detritus and coral rubble in tropical coastal regions of the Caribbean Sea (Faust, 1997).

Prorocentrum norrisianum