**2. Materials and Methods**

Quantitative samples were taken in June 2018, in the intertidal zone at Shinyang, close to the eastern corner of Jeju Island (Figure 1). Sediments were fixed in 5% neutralized formalin solution and brought back to the laboratory. Meiofauna were extracted using the Ludox method [11], and postfixed with 70% ethanol dyed with Rose bengal. Nematodes were counted and specimens were packed into a Syracuse glass filled with mixture of glycerin, 95% ethanol, and distilled water (1:29:70). The glass was placed in a drying oven set to 40 ◦C for 1–2 days until completely dehydrated, as in the glycerin-ethanol method [12]. Specimens were mounted in a drop of anhydrous glycerin within a wax-paraffin ring. Specimens were identified, measured, photographed, and drawn under a Leica DM5000 light microscope equipped with Leica Application Suite Version 3.8.0 software and a Leica DFC 425 C digital camera. All the measured sizes are given in μm. For scanning electron microscopy, specimens were dehydrated in a series: 40% ethanol, 70% ethanol, 95% ethanol, 95% ethanol + acetone (50:50), acetone I, and acetone II, and then critical point dried. Once dried, specimens were mounted on a stub to be coated with platinum–palladium alloy and examined with Cam Scan S-2.

**Figure 1.** Map of sampling locality. This map is made with QGIS software v.2.18.14, a free and open-source geographic information system (https://qgis.org).

Type specimens were deposited in National Institute of Biological Resources (South Korea).
