The morphological features of germling cells were examined to identify an unspecified resting cyst (described as Cochlodinium cf. polykrikoides-like resting cyst) in the Korean coastal area. LSU rRNA gene sequences were also obtained from a strain established from the germling cells. The resting cysts isolated from Korean coastal sediment were characterized as being brown in color, having a large dark-red body, and fibrous lobed ornaments. The germling cells were ellipsoidal with an irregular outline and had an open comma-shaped ASC (apical structure complex), a wide and deep cingulum, and a deep sulcus. These morphological features were consistent with those of previously described harmful dinoflagellate Pseudocochlodinium profundisulcus. The molecular phylogeny revealed that the germling cells and P. profundisulcus were conspecific. Based on these morphological and phylogenetic data, this study documents the occurrence of P. profundisulcus in a Korean coastal area for the first time.

1. INTRODUCTION
2. MATERIALS AND METHODS
    2.1. Sediment collection and cultureestablishment
    2.2. Light microscopy (LM)
    2.3. Scanning electron microscopy (SEM)
    2.4. DNA extraction and sequencing
    2.5. Sequence alignment and phylogeneticanalysis
3. RESULTS AND DISCUSSION
    3.1. Morphological features of a resting cystand germling cell
    3.2. Phylogenetic positions of germling cells
CRediT authorship contribution statement
Declaration of Competing Interest
ACKNOWLEDGEMENTS
REFERENCES

• Joo Yeon Youn(Library of Marine Samples, Korea Institute of Ocean Science and Technology, Geoje 53201, Republic of Korea)
• Kyong Ha Han(Library of Marine Samples, Korea Institute of Ocean Science and Technology, Geoje 53201, Republic of Korea, Department of Environmental Science, Hanyang University, Seoul 04763, Republic of Korea)
• Kyeong Yoon Kwak(Library of Marine Samples, Korea Institute of Ocean Science and Technology, Geoje 53201, Republic of Korea)
• Hyeon Ho Shin(Library of Marine Samples, Korea Institute of Ocean Science and Technology, Geoje 53201, Republic of Korea) Corresponding author