Faunistic survey on freshwater annelids from Korea

Aquatic oligochaetes are an important organism in freshwater ecosystem. They are found in almost all fresh­ water environments and could be dominant in their hab­ itats depending on surrounding conditions (van Haaren, 2002; Behrend et al., 2009; Ragonha and Takeda, 2014). These worms act as mediators between the primary producers and the upper consumers, decomposers, or some times intermediate hosts of parasites in freshwater ecosystems (Pandit, 1980; Gardner et al., 1981). And withstanding water pollution, some species are preferred as biological indicators for freshwater environments (Chakrabarty and Das, 2006; Ferreira et al., 2011). Oligochaetes are known for more than 5,000 species around the world. Of these, approximately 1,600 spe­ cies are found in freshwater environment (Martin et al., 2008). Faunistic studies on freshwater oligochates have been actively carried out in the East Asian regions main­ ly by scientists of China and Japan (Hatai, 1898; Chen, 1940). Consequently, about 319 species and 438 species have been reported in China and Japan, respectively (Ohtaka and Nishino, 1999; 2006; Wang and Cui, 2007; Cui et al., 2008; 2015; Cui and Wang, 2009a; 2009b; He et al., 2010; Ohtaka, 2012; 2014; Pan et al., 2014). Riverine system of the Korean peninsula is composed of several geographically separated freshwater systems, each of which shows its unique freshwater fauna. There­ fore, this peninsula possesses biological diversity more than expected (Jung et al., 2009). Nonetheless, study of aquatic oligochaete fauna in Korea is still in its begin­ ning stages compared to those of China and Japan. In Korea, the number of reliable species of aquatic oligo­ chaetes is around 48 species (Brinkhurst et al., 1994; Yoon et al., 2000; Jung, 2011; 2012; Park et al., 2013a; 2013b; Lee and Jung, 2014a; 2014b; 2015). Here, we re­ port twenty­two species of aquatic annelids ­ 20 species of oligochaetes and one species of aelosomatid ­ as a result of faunistic studies on specimens collected during nationwide surveys conducted from 2013 to 2014.