Phylogenetic Systematics of Onychophorans and Opiliones

Velvet worms (Onychophorans) and harvestmen (Opiliones) occupy pivotal positions in the evolution of panarthropods and offer unique insights into the early colonisation of land by arthropods. Traditionally, morphological characters have underpinned their classification, but homoplasy and limited character sets have hindered resolution at deeper nodes. The advent of next-generation sequencing has ushered in a phylogenomic era, integrating transcriptomes, ultraconserved elements and genome-wide markers to reconstruct robust evolutionary trees. In Onychophora, these approaches have clarified relationships within Peripatidae and Peripatopsidae, revealed cryptic species diversity, traced shifts in reproductive modes and underscored Gondwanan vicariance patterns. In Opiliones, comprehensive transcriptomic sampling across all suborders has stabilised familial and higher-level placements, while molecular dating calibrated against fossils has converged on Ordovician–Devonian origins and illuminated subsequent radiations linked to ancient continental break-up. Together, these advances enhance our understanding of terrestrialisation, morphological evolution and biogeography, informing biodiversity conservation and comparative studies across Arthropoda.

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Phylogenetic Systematics of Onychophorans and Opiliones publication trend

The graph below shows the total number of articles in phylogenetic systematics of onychophorans and opiliones across all publications each year (not limited to Nature Index journals).

Technical terms

Phylogenomics: The study of evolutionary relationships using genome-scale data to resolve phylogenetic trees.

Transcriptomics: Sequencing and analysis of the complete set of RNA transcripts to infer gene expression and genetic markers for phylogeny.

Ultraconserved elements (UCEs): Highly conserved regions of the genome used as anchors for comparative sequence analyses across taxa.

Vicariance: Geographic separation of populations by physical barriers leading to lineage divergence.

Molecular clock: A method that estimates divergence times by correlating genetic change with chronological time, calibrated by fossil or geological events.

References

1. Phylogenomic Analysis of Velvet Worms (Onychophora) Uncovers an Evolutionary Radiation in the Neotropics. Molecular Biology and Evolution (2021).
2. Cryptic Speciation in Brazilian Epiperipatus (Onychophora: Peripatidae) Reveals an Underestimated Diversity among the Peripatid Velvet Worms. PLOS ONE (2011).
3. The Opiliones tree of life: shedding light on harvestmen relationships through transcriptomics. Proceedings of the Royal Society B (2017).
4. A revised dated phylogeny of the arachnid order Opiliones. Frontiers in Genetics (2014).
5. A stable phylogenomic classification of Travunioidea (Arachnida, Opiliones, Laniatores) based on sequence capture of ultraconserved elements. ZooKeys (2018).