Taxonomy and systematics of dragon millipedes genus desmoxytes chamberlin, 1923 in Thailand

Abstract

Taxonomy and systematics of the dragon millipede genus Desmoxytes sensu Golovatch & Enghoff (1994) (= Desmoxytes s.l.) of the family Paradoxosomatidae has been analyzed and implemented based on an integrative approach by morphological revision and molecular phylogeny from three partial genes (COI, 16S rRNA and 28S rRNA). The specimens were collected mainly from Thailand and neighboring countries in mainland Southeast Asia, and were compared with available type material. Taxonomic revision resulted in the subdivision of Desmoxytes s.l. into five genera, viz., Desmoxytes s.s., Hylomus stat. rev., Nagaxytes gen. nov., Gigaxytes gen. nov. and Spinaxytes gen. nov. All five genera showed distinctive morphological characteristics in agreement with high genetic divergences. The total number of dragon millipedes is currently brought up to 68: eighteen species in Desmoxytes s.s.; four species in Nagaxytes; four species in Gigaxytes; four species in Spinaxytes and 33 species in Hylomus. In this study, 27 species have been described as new species to science, of which 23 species are recorded from Thailand, two from Myanmar and two from Malaysia. Almost all species were found in limestone habitats; a few species inhabit tropical forest. All are regarded as locally endemic species according to their narrow distribution (except the tramp species D. planata). The molecular phylogeny indicates paraphyly of Desmoxytes s.l. in terms of the outgroup genus Orthomorpha. The proposed tree delimits five clades of dragon millipedes corresponding to the five genera in accordance with the morphology-based classification and splitting approach. Each of the five genera was recovered as monophyletic in both Maximum Likelihood and Bayesian Inference analyses, and the results also support the significance of male genitalia (gonopod) and paraterga as diagnostic characters for genus identification. The results of the phylogenetic analysis interestingly show a high degree of compatibility between genetic structure and geographical distribution. Some biological traits such as mite and fungal associations were recorded for the first time in several species of these animals. By conducting the most comprehensive sampling of the dragon millipede to date, this study significantly expands the scope of morphological and molecular explorations, and reveals a much richer species diversity than previously known, finally leading to understanding of the relationships in this spectacular group of millipedes.