Phylogenetic relationships of millipedes in the subclass Penicillata (Diplopoda) with a key to the genera

ABSTRACT

Bristly millipedes (subclass Penicillata, order Polyxenida) are minute diplopods characterised by uncalcified cuticle and a body covered with unique tufts of bristles. The order is found worldwide and comprises less than 200 described species divided into three families, with many of the species and genera being poorly known. The first evolutionary analysis of the order presented here utilises both molecular (COI, 18S rRNA and 16S rRNA) and morphological data to examine monophyly of the families and subfamilies and the evolutionary relationships between them. Maximum likelihood analysis was based on molecular data only, whereas parsimony analyses were based on molecular data as well as combined morphological and molecular data. The results of these analyses with two different optimality criteria were incongruent in many aspects. Unlike parsimony, the likelihood result found strong support for a basal position of the family Synxenidae and separation of the order into two monophyletic clades corresponding to the two superfamilies Synxenoidea, containing the family Synxenidae, and Polyxenoidea, containing the families Polyxenidae and Lophoproctidae. Parsimony results did not support the existence of the two superfamilies. Both analyses resolved the family Synxenidae as monophyletic and Polyxenidae as polyphyletic, whereas the family Lophoproctidae was shown to be paraphyletic in likelihood and monophyletic in parsimony analysis. The subfamilies Monographinae and Polyxeninae were found to be monophyletic in the likelihood tree but parsimony suggested paraphyly of both. The results suggest that further revision of the systematics of the Polyxenida may be necessary. However, a much larger molecular data set will be necessary to clarify and provide stronger nodal support for phylogenetic trees and to confirm the relationships, particularly of the families Polyxenidae and Lophoproctidae. Molecular identification is likely to be an important tool for this taxonomically challenging order in future. A simplified key to the genera is provided.

KEYWORDS:

• Diplopoda
• Polyxenida
• bristly millipedes
• morphology
• phylogeny
• identification key

Acknowledgements

We thank Stella Loke, for her advice and encouragement to MS, and Greg Edgecombe for guidance to MS in setting up the morphological matrix. We are grateful to Julianne Waldock, Gaynor Dolman, Graham Milledge, Owen Seeman, Monique Duy-Jacquemin, Sergei Golovatch, Ivan Tuf and Dmitry Shcherbakov for provision of material. We also wish to thank Prof. Sergei Golovatch and one anonymous reviewer for their comments that helped to refine this article.

Disclosure statement

No potential conflict of interest was reported by the authors.

supplementary material

The supplementary material for this article can be accessed here.

Additional information

Funding

Dimitry Shcherbakov was supported by RFBR [grant 13-04-01839] for his collecting trip to South America.