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The diversity of centric diatoms is documented for the transitional zone of the lower part of the Southern Bug River (Ukraine) just before entering the Dnipro-Bug Estuary and compared to earlier results from the upstream sampling sites of the same river system. Benthic samples of the following sites were investigated: north of Mykolaiv City (approximately 5 km), in Mykolaiv City (near Varvarivskyi Bridge), and 5 km south of the city. Twenty-four centric diatom taxa belonging to 11 genera were identified, analysed, and documented by scanning electron microscopy (SEM) and light microscopy (LM). Among them, Aulacoseira nivalis is the first report for Ukraine, A. islandica and is the first confirmed record for the studied area since the 1930s. The maximum number of centric diatom taxa found in one station was 21, the minimum 10. Melosira subglobosa was the most common (documented in 57–80% of sites with centric diatoms) and abundant species 7.3–15.7% in relative abundance to all diatom taxa. The discovered diversity of taxa and its comparison with previous results is discussed with regard to the relevance of estuary zones in the research of diatoms.

The epiphytic diatoms attached to seaweeds and benthic diatom assemblages, have been collected along the Seogwipo coast in Jeju Island, South Korea. In the last three-year survey, 80 diatom taxa inhabiting warmer oceans have been found, including those in the tropical and subtropical regions such as the Pacific Ocean, the Caribbean Sea, the western Indian Ocean, and other warmer regions. These diatom flora shows a worldwide pattern that concentrated around the Tropic of Cancer. This survey of local areas reveals the existence of many rare or retrieved taxa that were not well known until recently. Furthermore, some of them, including Aulacodiscus affinis, Leudugeria janischii, Hyalosynedra lanceolata, Trachyneis velata var. ornata, Lyrella concilians have been reported for the first time since the first entry or haven been reported only once. Of the diatom flora described here, 48 taxa are new to South Korea and previously unrecorded in the local area.

2. Aulacodiscus orientalis Greville (Fig. 9) Type locality: Ceylon. References: Schmidt et al. 1874–1959, pl. 34, figs 1–3; Williams 1988, p.15, pl. 17, figs 1–3; Lobban et al. 2012, p. 249, pl. 5, figs 3–5. Morphometrics: Valves 187 (85–140) μm, striae radiate from the center, 5 in 10 μm, areolae 3.5 in 10 μm on a stria. Thirteen pseudocelli on elevations in the corner of valve. Remarks: Aulacodiscus orientalis was reported in some places, North Celebes of Indonesia and Hawaiian Islands (Schmidt et al. 1874–1959), mangrove swamps of South Nigeria (Mills 1932), Guam in the western Pacific Ocean (Lobban et al. 2012), and the western coast of India (Sushanth and Rajashekhar 2012). This taxon is a typical one inhabiting warmer oceans. It was encountered once in this sampling areas, the Seogwipo coast, representing a new record for South Korea., Published as part of Joh, Gyeongje, 2021, Distribution and frequent occurrence of diatom taxa (Bacillariophyta) inhabiting warmer oceans in Seogwipo coast of Jeju Island, southernmost Korea, pp. 1-67 in Phytotaxa 517 (1) on page 7, DOI: 10.11646/phytotaxa.517.1.1, http://zenodo.org/record/8061058, {"references":["Williams, D. M. (1988) An illustrated catalogue of the type specimens in the Greville diatom herbarium. Bulletin of the British Museum (Natural History), Botany 18 (1): 1 - 148.","Lobban, C. S., Schefter, M., Jordan, R. W., Arai, Y., Sasaki, A., Theriot, E. C., Ashworth, M., Ruck, E. C. & Pennesi, C. (2012) Coral-reef diatoms (Bacillariophyta) from Guam: new records and preliminary checklist, with emphasis on epiphytic species from farmer-fish territories. Micronesica 43: 237 - 479.","Mills, F. W. (1932) XXI. - Some diatoms from Warri, South Nigeria. Journal of the Royal Microscopical Society 52: 383 - 394. https: // doi. org / 10.1111 / j. 1365 - 2818.1932. tb 01887. x"]}

1. Aulacodiscus affinis Grunow (Figs 10, 11) Type locality: Gaz. Exped.; Japan. References: Schmidt et al. 1874–1959, pl. 34, figs 9, 10; Siqueiros-Beltrones & Argumedo-Hernández 2014, figs 26–28. Morphometrics: Valves 113–178 μm in diameter, striae radiate from the center, 5–8 in 10 μm, areolae 3–5 in 10 μm on a stria. Eight pseudocelli on elevations in the corner of valve. Remarks: Aulacodiscus affinis is very rare worldwide and its existence is not well known. This taxon was only reported from a few localions worldwide, including the Pliocene sediments of Shikotan Island and Lesser Kuril Ridge in Russia (Terekhov et al. 2011), and from Magdalena Bay along the western coast of the Baja California Peninsula in Mexico as epiphytes on red seaweed (Siqueiros-Beltrones and Argumedo-Hernández 2014). It was also very rare in diatom assemblages obtained from the Seogwipo coast, Jeju Island, representing a new record for South Korea., Published as part of Joh, Gyeongje, 2021, Distribution and frequent occurrence of diatom taxa (Bacillariophyta) inhabiting warmer oceans in Seogwipo coast of Jeju Island, southernmost Korea, pp. 1-67 in Phytotaxa 517 (1) on page 7, DOI: 10.11646/phytotaxa.517.1.1, http://zenodo.org/record/8061058, {"references":["Siqueiros-Beltrones, D. A. & Argumedo-Hernandez, U. (2014) Particular structure of an epiphytic diatom assemblage living on Ploclamium cartilagineum (Lamoroux) Dixon (Rhodophyceae: Gigartinales). CICIMAR Oceanides 29: 11 - 24. https: // doi. org / 10.37543 / oceanides. v 29 i 2.136","Terekhov, E. P., Tsoy, I. B., Mozherovskii, A. V. & Vagina, N. K. (2011) Pliocene sediments of Shikotan Island (Lesser Kuril Ridge). Stratigraphy and Geological Correlation 19: 337 - 351. https: // doi. org / 10.1134 / S 0869593811030105"]}