Taxonomy and systematics of terrestrial earthworm genera Amynthas Kinberg, 1867 and Metaphire Sims and Easton, 1972 in Thailand

Abstract

Taxonomy and systematics of two main earthworm genera of the family Megascolecidae has been carried out and analyzed in Thailand. The previous reports confirmed the total number of 29 nominal species which 18 belonging to the genus Amynthas and 11 to the genus Metaphire. After making additional 123 collecting sites and carefully examining principal morphological characters such as the male pore area, spermathecae, genital markings, testes, seminal vesicles, prostate gland and intestinal caeca. The total number of 44 nominal species and three undescribed have been confirmed and reported. Of which, two are newly record to Thailand: Amynthas andersoni (Michaelsen, 1907) and A. corticis (Kinberg, 1867), while three are considered to be peregrine species. There are A. corticis (Kinberg, 1867), A. morrisi (Beddard, 1892) and A. gracilis (Kinberg, 1867). In additional, fourteen species have been described containing seven from each genus. The re-descriptions of the type species of the genus Amynthas, A. aeruginosus Kinberg, 1867 has also been written. The total number has finally been clarified as 26 and 18 species of the genera Amynthas and Metaphire respectively. The phylogenetic analysis using COI and ITS2 genes has been analyzed and using 27 operational taxonomic units (OTUs), consisting of 15 species of Amynthas and 12 species of Metaphire. The results were largely congruent with morphological identified species. However, some possible cryptic speciation has been noticed in Metaphire houlleti species complex, which probably contains at least three distinct species. Phylogenetic relationships between the two genera still have not been resolved clearly. The relations are not monophyly, but interpreted as polyphyly and/or paraphyly groups. However the closed relationships have been found in many cases such as Amynthas thakhantho and A. turris; Metaphire peguana and M. bahli which showing monophyletic relationships. The adding taxa and sampling localities and also genes may be interpreted the better distinct phylogenetic analysis.