The Hangang River* is necessary to manage the water environment of severe pollution due to the high density of residential areas, parks, and agriculture and the large population concentrated there. Benthic macroinvertebrates, such as chironomids larvae, are bioindicator species that reflect environmental changes and are crucial for water quality monitoring. In this study, we investigated morphological characteristics and molecular analysis of the chironomids larvae inhabiting the Hangang River area for water environment surveys. For this research, 20 rivers, lakes, and urban area in the Hangang River basin were selected. Chironomids larvae were collected from July to September 2022, and their appearance and characteristics were identified through morphological identification. In addition, phylogenetic analysis was performed based on the mtCOI gene sequences of the collected chironomids larvae, and identification at the genus level was confirmed. As a result, 32 species and 18 genera of 3 subfamilies of Chironomidae larvae were identified, and Stictochironomus sp. dominated most sites (6 sites). The morphological characteristics of the identified chironomids larvae, such as the mentum, ventromental plate, and antenna, were organized into table and pictorial keys, and a Bayesian inference molecular phylogeny was presented. These results provide basic morphological information for genus-level identification and can be used as fundamental information for water quality management. *The public nomenclature following by NGII 2015

Members of the non-biting midge family Chironomidae are the most widespread and abundant group of aquatic insects in fresh waters. Although the composition of chironomid communities is considered to be a potential biotic index for water quality assessment, it has not been used easily because of the difficulties with species level identification for larvae. This study was to analyse the molecular operational taxonomic units (MOTU) in chironomid communities to appropriately apply a species level identification. A total of 41 chironomid larvae collected from 7 sampling sites in the Han river system according to water quality were used for analyses. Partial mitochondrial DNA cytochrome c oxidase I (COI) genes were sequenced and analyzed. As a result, 35 different haplotypes (MOTU01-13) were obtained from the 673bp COI sequences. Average genetic distance was 0.0041 (range 0.000 to 0.013) within the MOTU and was 0.1703 (range 0.1181 to 0.2456) between the MOTUs. Nine MOTUs were found at the stream sites represented water quality A, 2 MOTUs at water quality C, and 1 MOTU at water quality D.