The oligochaete worms in the genus Nais are common to freshwater habitats. These worms have a highly-developed prostomium and pigmented eye spots. All species have hair chaetae, bifid or single pointed needle chaetae on the dorsal side and ventral chaetae beginning in II with bifid crotchets. Most species of Nais genus live in areas where bottom is covered by sand, gravel or organic matter in aquatic plants. Currently, 26 species of Nais have been recorded worldwide. From the recent faunal studies, 3 species of Nais have been newly reported in Korea. Here, we newly report 6 species of Nais with diagnosis, illustrations and identification keys to Korean Nais species: N. behningi, N. pseudobtusa, N. simplex, N. bretscheri, N. stolci and N. elinguis.

Aquatic oligochaetes were investigated from a small amount of sediment sampled from the Jung-nang Stream, an urban stream in Seoul, Korea, in November 2012. Sorted oligochaetes were observed under alight microscope in a drop of carbonated water, and then preserved in 70% ethanol. Some specimens were slidemounted using glycerin and Eupharal. As a result, the following 12 species were identified including 8 newKorean records, Bothrioneurum vejdoskyanumStolc, Branchiodrilus hortensis(Stephenson), ChaetogastercristalinusVejdosky, Nais communisPiguet, Nais pardalisPiguet, Dero obtusad’Udekem, PiguetielladenticulataLiang, and Haemonais waldvogeli Brescher and 4 additional known species, Limnodrilus hoffmeisteriCleparéde, Branchiura sowerbyi Beddard, Chaetogaster diastrophus(Gruithuisen), and Stylaria fossularisLeidy.This study shows how freshwater oligochaetes are diverse even in urban streams in Korea, if a propersamplingand examining method is employed.

Up to now the complete mitochondrial genome (mitogenome) sequences of only three species of clitellate have been available. We have determined the complete mitogenome sequences of the elusive Burmese giant earthworm Tonoscolex birmanicus (Clitellata: Megascolecidae), which is endemic to Myanmar. The 15,170-bp long genome contains the 37 genes typical of metazoan mitogenomes [13 protein-coding genes (PCG), two rRNA genes and 22 tRNA genes] and one major non-coding region. All of the 37 genes are transcribed from the same DNA strand. The arrangement of the T. birmanicus mitogenome is identical to that of two within-ordinal species Lumbricus terrestris and Perionyx excavates. All 13 PCGs start with the ATG. For the stop codon, only six PCGs end with the TAA, whereas the remaining ones ends with the incomplete stop codon, T. Genes overlap in a total of 14 bp in five locations, and harbor a total of 16 bp of intergenic spacer sequences in nine locations.