Prorocentrum lima (Ehrenberg) Dodge, 1975
Species Overview:
Prorocentrum lima is an armoured, marine, benthic dinoflagellate species with world-wide distribution.
Taxonomic Description:
P. lima is a bivalvate species often observed in valve view. Cells are oblong to ovate, small to medium-sized, broadest in the mid-region, and narrow toward the anterior end (Figs. 1-4). Cell size ranges between 32-50 µm in length and 20-28 µm in width. Thecal valves are thick and smooth with scattered surface pores (Figs. 1-4). Each valve contains about 50-80 small round marginal pores evenly spaced around the perifery of the valve (0.6 µm in diameter) (Figs. 1,3), and about 60-100 larger round to oblong unevenly distributed valve pores with trichocysts (0.48 µm in diameter) (Figs. 1-3). All pores have smooth edges (Figs. 1,2,5). The center is devoid of pores (Figs. 1-3). The presence of marginal pores has proven to be a useful diagnostic feature of P. lima distinguishing this species from other Prorocentrum species. Occasionally P. lima can be found without marginal pores or with partially filled pores. In older cells, the thecal surface can become vermiculate. The intercalary band appears as a thick, smooth and well-defined margin at the periphery of the valve; it can give the appearance of a flared ridge (Figs. 1,2,6,7) (von Stosch, 1980, Dodge, 1975, Faust, 1990b, Faust, 1991, Steidinger and Tangen, 1996).
The periflagellar area is a shallow V-shaped depression on the right valve made up of eight platelets and two pores: a larger flagellar pore and a smaller auxiliary pore (Fig. 5). A protruding periflagellar collar surrounds the auxiliary pore (Fig. 5). Both valves are anteriorly indented; the left valve margin has a flattened apical ridge that borders the periflagellar area (Figs. 1,5,7) (Faust, 1991, Steidinger and Tangen, 1996).
Morphology and Structure:
Prorocentrum lima is a photosynthetic species containing two chloroplasts, a central pyrenoid and a large posterior nucleus (Figs. 6,7) (Dodge, 1975).
Reproduction:
Prorocentrum lima reproduces asexually by binary fission in which each new daughter cell sheds the parent cell theca and produces two new valves. This species also exhibits an alternate form of asexual reproduction in which a chain of cell pairs is enclosed within a thin-walled cyst. In this mode multiple vegetative divisions occur within a hyaline envelope, a division cyst, which may contain a chain of 4 to 32 cells (Figs. 8,9) (Faust, 1993d). Sexual reproduction has also been documented in this species: isogamous gametes form, conjugation occurs, and a triple-layered hypnozygote (resting cyst) is produced (Fig. 10) (Faust, 1993c).
Species Comparison:
P. lima is difficult to identify due to its similar morphology to several other Prorocentrum species with a triangular periflagellar area and an oval or ovoid shape (e.g. P. foraminosum, P. concavum and P. hoffmannianum). P. lima can be distinguished by its size, shape, narrow periflagellar area and the presence of valve and marginal pores. P. concavum, however, is larger, broader, has more valve pores and does not have marginal pores. P. foraminosum and P. hoffmannianum are also similar in shape to P. lima, though both are larger species with very different valve pore numbers and arrangements. P. hoffmannianum, moreover, is much broader and its valve surface is deeply areolated (Steidinger, 1983, Steidinger and Tangen, 1985, Steidinger and Tangen, 1996, Fukuyo, 1981, Faust, 1990b, Faust, 1991, Faust, 1993b).
Steidinger, 1983 recognized that the marginal pores of P. lima can be used to differentiate this species at the light microscope level from completely areolated species such as P. concavum or P. compressum which are similar in shape.