Megascolex (Perichaeta) diffringens Baird, 1869 and Pheretima pingi Stephenson, 1925 types compared to the Amynthas corticis (Kinberg, 1867) and A. carnosus (Goto & Hatai, 1899) species-groups (Oligochaeta: Megadrilacea: Megascolecidae)

Amynthas diffringens (Baird, 1869) is deemed valid yet comparable to A. corticis (Kinberg, 1867) and to A. nipponicus (Beddard, 1893) or A. peregrinus (Fletcher, 1896). Its syntypes tend to more genital markings than usual as shown for variable specimens from Japan, Korea, and Australasia that comply genetically with either of two A. corticis spp. groups. A. diffringens type-locality was UK hothouses yet closest specimens appear in part of A. heteropodus (Goto & Hatai, 1899) (=A. corticis) from Japan. Japanese Amynthas divergens (Michaelsen, 1892) is restored based on its serrate intestinal caeca. Meanwhile, the lectotype of Amynthas pingi (Stephenson, 1925) is deemed a synonym of A. carnosus (Goto & Hatai, 1899) compliant with Kobayashi's (1936) types III & II. Erstwhile A. pingi synonym A. fornicatus (Gates, 1925) is again included, but A. hongkongensis (Michaelsen, 1910) and A. chungkingensis (Chen, 1936) are provisionally retained whilst A. carnosa lichuanensis Wang & Qiu, 2005 is given separate species status. A new Korean taxon is proposed as A. carnosus naribunji sub-sp. nov. and two replacement names are provided: A. zhuya nom. nov. for homonym A. montanus Qiu & Sun, 2012 from Hainan and A. yizhou for A. carnosus sensu Shen et al., 2005 from Taiwan. No attempt is made to fully resolve numerous Japanese synonyms of A. carnosus [eg Ishizuka's (2001) invista, subterranea, subalpina, umbrosa, mutabilis, nubicola, plus A. nonmonticolus Blakemore, 2010] nor Korean synonyms [eg kyamikia Kobayashi, 1934, monstrifera Kobayashi, 1936 and murayamai Kobayashi, 1938, sangyeoli, youngtai (with segments miscounted), kimhaeiensis, sinsiensis and baemsagolensis - all names by Hong & James (2001) plus ?A. sangumburi Hong & Kim, 2002 (its segments miscounted too)] also A. fuscus Qiu & Sun, 2012 from Hainan and Taiwanese monsoonus James et al., 2005 plus A. penpuensis Shen et al., 2003 and A. taiwumontis Shen et al., 2013 syns. nov.. All synonyms remain in the currently defined A. carnosus pending full revisons although several may eventually comply with parts of prior A. corticis s. lato.