Ultrastructure and Systematics of Two New Species of Dinoflagellate, Paragymnodinium Asymmetricum sp. nov. and Paragymnodinium Inerme sp. nov. (Gymnodiniales, Dinophyceae)1.

Abstract

The genus Paragymnodinium currently includes two species, P.shiwhaense and P.stigmaticum, that are characterized by mixotrophic nutrition and the possession of nematocysts. In this study, two new dinoflagellates belonging to this genus were described based on observations using LM, SEM, and TEM together with a molecular analysis. Cells of P.asymmetricum sp. nov., isolated from Nha Trang Beach, Vietnam, were 7.9-12.6μm long and 4.7-9.0μm wide. The species showed no evidence of feeding behavior and was able to sustain itself phototrophically. Paragymnodinium asymmetricum shared many features with P. shiwhaense, including presence of nematocysts, absence of an eyespot, and a planktonic lifestyle, but was clearly distinguished by the asymmetric shape of the hyposome, possession of a single chloroplast, and its nutritional mode. Cells of P.inerme sp. nov., isolated from Jogashima, Kanagawa Pref, Japan, were 15.3-23.7μm long and 10.9-19.6μm wide. This species also showed no evidence of feeding behavior. Paragymnodiniuminerme was similar to cells of P.shiwhaense in shape and planktonic lifestyle, but its nutritional mode was different. The presence of incomplete nematocysts was also a unique feature. A phylogenetic analysis inferred from concatenated SSU and LSU rDNA sequences recovered the two dinoflagellates in a robust clade with Paragymnodinium spp., within the clade of Gymnodinium sensu stricto. This evidence, together with their morphological similarities, made it reasonable to conclude that these two dinoflagellates are new species of Paragymnodinium.