MORPHOLOGY OF CIGUATERA-CAUSING PROROCENTRUM-LIMA (PYRROPHYTA) FROM WIDELY DIFFERING SITES

Clones of ciguatoxigenic Prorocentrum lima (Ehr.) Dodge 1975 were examined from different geographical areas (Pacific and Atlantic oceans) and compared with the earliest descriptions between 1881 and 1933 and light and electron micrographs of other researchers. Surface morphology of the widely distributed clones was remarkably similar, and morphological variability of ecotypes of this species is minimal. The number of valve pores (58-85 per valve) and marginal pores (55-72 per valve) is characteristic of the species. Marginal pores are located adjacent to the intercalary band in a regular pattern, are readily distinguishable by light microscopy, and are a good criterion for identifying P. lima. The periflagellar area of P. lima is a unique taxonomic feature; however, it can only be seen with the scanning electron microscope at high magnification. The anterior periflagellar area is a broad triangule, where the left valve margin is flat and the right valve has a V-shaped depression. It accommodates a flagellar and an auxiliary pore and a flared, protuberant apical collar enclosed by eight small plates. The protuberant apical collar of P. lima has only been observed in one other Prorocentrum species, P. hoffmannianum, which has an areolated valve surface. In contrast, the valve surface of P. lima is smooth. Cells possess chloroplasts, a centrally located pyrenoid, a posterior nucleus, and two flagella. The shape and size of P. lima are variable and less useful for identifying specimens.