Prorocentrum shikokuense Hada and P. donghaiense Lu are the synonym of P. obtusidens Schiller (Prorocentrales, Dinophyceae)

Abstract

In Japanese, Chinese and Korean coastal waters, a small thecate Prorocentrum species has been recognized as the bloom forming species. However, the species has been called as P. shikokuense, P. donghaiense and P. dentatum, respectively, despite their morphological similarity and identical rDNA sequences. To resolve the confusion, we examined the morphological features including architectural details of the periflagellar area and molecular phylogeny of the isolates collected from East China Sea and Korean coast, and reviewed the taxonomic descriptions of the confused species and the related species and its historical records. Morphology and phylogeny based on SS U, ITS region and LSU rDNA sequences revealed that the confused species and our isolates are conspecific and morphological features of P. dentatum recorded in the phylogenetic trees does not coincide with those of the originally described P. dentatum. Dodge (1975) included P. veloi, P. monacens and P. obtusidens to P. dentatum as synonyms, however the literature review revealed that the morphological features of his specimens were closer to those of P. obtusidens in the original description, rather than those of originally described P. dentatum and that P. obtusidens is distinguished from P. dentatum by relatively small size, the parallel sides toward the anterior, blunt anterior extension on one side and probably location of nucleus. This indicates that P.