Abstract
A heterotrophic dinoflagellate isolated from the waters of Masan Bay, Korea was, at first glance, morphologically similar to Katodinium glandulum, yet had unreported plate patterns and DNA sequences. This dinoflagellate had thin plates arranged in a Kofoidian series Po, X, 4′, 2a, 6″, 6c, PC, 3+s, 5‴, 0p, and 2⁗, similar to species in the family Pfiesteriaceae. However, it did not have a closing plate (cp) and only small sulcal plates (3+s). Furthermore, this dinoflagellate had a conspicuous apical hook (finger-like projection) on the epitheca, like K. glandulum and Katodinium asymmetricum, but unlike the other Katodinium species and the other species in the family Pfiesteriaceae. The epitheca had a conical shape and was markedly larger than the hemispherical hypotheca. Cell lengths and widths of live biflagellate cells satiated with the phototrophic dinoflagellate Heterocapsa triquetra were 21.2–29.2μm and 18.1–24.9μm, respectively, while those of biflagellate cells starved for 4d were 10.2–17.3μm and 7.7–14.6μm, respectively. The ratio of the width of the epitheca relative to the hypotheca (0.9) is similar to that of K. glandulum, but larger than that of K. asymmetricum (0.5–0.7). The dinoflagellate had a peduncle but lacked an eyespot. The DNA sequences differed from those of K. glaucum, the only Katodinium species with reported rDNA sequences. Compared to the other known genera in the family Pfiesteriaceae, the rDNA sequences of the small subunit (SSU), ITS regions (ITS1, 5.8S, ITS2), and D1–D3 large subunit (LSU) differed by 1.9–6.8%, ≥4.4%, and ≥5.6%, respectively. In a phylogenetic tree based on the SSU and LSU rDNA, a clade containing this species belonged to a larger clade of the family Pfiesteriaceae, but was divergent from a clade containing K. glaucum. Due to its morphological similarity to K. glandulum and genetic differences from K. glaucum and the other species in the family Pfiesteriaceae, it is proposed that this species Aduncodinium glandula be assigned to be a new genus and a new combination, A. glandula.
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