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 7.9–12.6 μm long and 4.7–9.0 μm 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 15.3–23.7 μm long and 10.9–19.6 μm wide. This species also showed no evidence of feeding behavior. Paragymnodinium inerme 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.

Paragymnodinium verecundum sp. nov. (Gymnodiniales, Dinophyceae), a new species of mixotrophic dinoflagellate from Japan

“…2010; Yokouchi et al . 2018, 2020). Paragymnodinium verecundum was demonstrated to be a sister of P. stigmaticum , the sole benthic, eyespot‐bearing species known to date in the genus Paragymnodinium (Yokouchi et al .…”

“…(2010), with the type species, Paragymnodinium shiwhaense Kang, Jeong, Moestrup & Shin, and has three additional currently accepted species, Paragymnodinium stigmaticum Yokouchi, Onuma & T. Horiguchi, Paragymnodinium asymmetricum Yokouchi, Takahashi, Nguyen, Iwataki & T. Horiguchi and Paragymnodinium inerme Yokouchi, Takahashi, Nguyen, Iwataki & T. Horiguchi (Yokouchi et al . 2018, 2020). They are all athecate, plastid‐bearing dinoflagellates, with a slightly curved or straight sulcal extension‐like furrow (SEF, sensu Kang et al .…”

“…2010; Yokouchi et al . 2018, 2020). Paragymnodinium is also characterized by the possession of nematocysts, a type of extrusome with a complex ultrastructure.…”

“…However, the other two species, P. asymmetricum and P. inerme , have never been observed to display feeding behavior and can be cultured successfully without prey, indicating phototrophic nutrition (Yokouchi et al . 2020). Paragymnodinium asymmetricum possesses nematocysts similar in structure to those of P. shiwhaense or P. stigmaticum , but P. inerme has only a few, with a collapsed structure, indicative of a loss in function (Yokouchi et al .…”

“…Paragymnodinium asymmetricum possesses nematocysts similar in structure to those of P. shiwhaense or P. stigmaticum , but P. inerme has only a few, with a collapsed structure, indicative of a loss in function (Yokouchi et al . 2020). Therefore, the genus Paragymnodinium includes species with different nutritional strategies and provides an opportunity to consider the evolutionary pathways of the nutritional mode.…”