**4. Conclusions**

The nematofauna of the intertidal sandy beach of Jeju Island is very rich, including over 70 species representing nearly all the families of marine free-living nematodes. Even described species of Thoracostomopsidae [5,6] and Selachinematidae (present paper) constitute only about one-third of the actual diversity of those families from the studied Jeju beach. In forthcoming works, we will try to identify at least the most common nematode species, aiming in the future to reveal fauna composition and species distribution from upper to lower intertidal horizons, as well as vertical distribution in sediment columns.

**Author Contributions:** Conceptualization, A.T. and W.L.; investigation, A.T. and R.J.; data curation, R.J. and W.L.; writing—original draft preparation, A.T.; writing—review and editing, R.J. and W.L.; funding acquisition, W.L. and A.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** The study was supported by a grant 18-504-51026 Russian Fund of Basic Research, a grant NRF-2017K2A9A1A06051528 from the Korea Research Foundation, a grant NIBR202000000 entitled "Study of Undiscovered Invertebrate Species from Korea" from the National Institute of Biological Resources (NIBR) funded by the Ministry of Environment (MOE) of the Republic of Korea, as well as by the Marine Biotechnology Program of the Korea Institute of Marine Science and Technology Promotion (KIMST) funded by the Ministry of Oceans and Fisheries (MOF) (No. 20170431).

**Acknowledgments:** The authors thank Vadim Mokievsky (P.P. Shirshov Institute of Oceanology, Moscow) and Jungho Hong (Biodiversity Institute, Marine Act Co., Seoul) for their help in the field work sampling in June 2018. The authors are grateful to both anonymous reviewers for their remarks and advice, which helped us amend the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **Abbreviations**


#### **References**


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