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Prey spectrum and feeding process of the mixotrophic thecate dinoflagellate Fragilidium mexicanum strain Fm-LOHABE01 were examined using a culture isolated from Masan Bay, Korea in 2011 during a summer bloom of the toxic dinoflagellate Alexandrium pacificum. The novel 18S and 28S rDNA sequences for F. mexicanum were also used to explore inter-species relationships within the genus Fragilidium. The F. mexicanum fed on species belonging to four dinoflagellate genera (i.e., Alexandrium, Ceratium, Heterocapsa, and Scrippsiella) when separately offered a variety of prey, including dinoflagellates, raphidophytes, cryptophytes, and a ciliate. In addition, F. mexicanum displayed different levels of feeding frequency for prey species of Alexandrium. While F. mexicanum consistently fed on A. catenella and A. pacificum, feeding on A. affine was rarely observed. The F. mexicanum ingested prey by direct engulfment through the sulcus, after capturing the prey by a tow filament. Phylogenetic analyses of 18S and 28S rDNA datasets demonstrated that Fragilidium sequences formed a monophyletic group with high statistical supports and diverged into four distinct clades. The F. mexicanum formed a separate clade with Fragilidium sp. EUSK D from Angola and Korean isolate of F. fissile with very strong supports., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The marine phototrophic dinoflagellate Gymnodinium smaydae n. sp. is described from cells prepared for light, scanning, and transmission electron microscopy. Also, sequences of the small (SSU) and large subunits (LSU) and the internal transcribed spacer region (ITS1-5.8S-ITS2) of ribosomal DNA were analyzed. This newly isolated dinoflagellate possessed nuclear chambers, nuclear fibrous connective, an apical groove running in a counterclockwise direction around the apex, and a major accessory pigment peridinin, which are four key features for the genus Gymnodinium. The epicone was conical with a round apex, while the hypocone was ellipsoid. Cells growing photosynthetically were 6.3-10.9 μm long and 5.1-10.0 μm wide, and therefore smaller than any other Gymnodinium species so far reported except Gymnodinium nanum. Cells were covered with polygonal amphiesmal vesicles arranged in 11 horizontal rows, and the vesicles were smaller than those of the other Gymnodinium species. This dinoflagellate had a sharp and elongated ventral ridge reaching half way down the hypocone, unlike other Gymnodinium species. Moreover, displacement of the cingulum was 0.4-0.6 × cell length while in other known Gymnodinium species it is less than 0.3 × cell length. In addition, the new species possessed a peduncle, permanent chloroplasts, pyrenoids, trichocysts, pusule systems, and small knobs along the apical furrow, but it lacked an eyespot, nematocysts, and body scales. The sequence of the SSU, ITS1-5.8S-ITS2, and LSU rDNA region differed by 1.5-3.8%, 6.0-17.4%, and 9.1-17.5%, respectively, from those of the most closely related species. The phylogenetic trees demonstrated that the new species belonged to the Gymnodinium clade at the base of a clade consisting of Gymnodinium acidotum, Gymnodinium dorsalisulcum, Gymnodinium eucyaneum, etc. Based on morphological and molecular data, we suggest that the taxon represents a new species, Gymnodinium smaydae n. sp., (© 2013 The Author(s) Journal of Eukaryotic Microbiology © 2013 International Society of Protistologists.)