Assessing troglomorphic and phylogenetically informative traits in troglobionts: a new cave-dwelling centipede illuminates the evolution of a soil-dwelling lineage (Chilopoda: Geophilidae)

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Cave-dwelling species are of special interest in evolutionary biology, because (i) many share particular traits associated with the cave habitat (troglomorphic traits), and (ii) some represent relict lineages that may conserve ancestral traits or possibly transitional traits, which may provide insights into the evolution of other highly derived species. However, these different kinds of characters are hard to assess thoroughly in troglobionts belonging to little known terrestrial arthropod groups. We describe a new species of centipedes from the Areias System caves, Brazil, namely, Plutogeophilus jurupariquibaba gen.n. sp.n., which adds to the few putative troglobionts known among Chilopoda Geophilomorpha. We analyzed a suite of characters in the light of a phylogenetic analysis and by direct comparison with epigean relatives, controlling for interindividual variation and its confounding sources. We found that: (i) troglomorphic traits of P. jurupariquibaba may include large body, elongate antennae, elongate legs and claws, and possibly also elongate setae and large coxal pores; (ii) the cave-dwelling Plutogeophilus is the sister lineage of the soil-dwelling Macronicophilus, whose morphology is highly derived and whose phylogenetic position remained unclear; (iii) compared with other extant geophilids, symplesiomorphic traits and apparently intermediate traits found in Plutogeophilus provide insights on the origin of the morphology of Macronicophilus, suggesting a stepwise modification of labrum, forcipular apparatus and ultimate legs, and the derivation of the unique rounded and spiny tip of the second maxillae from a pointed claw.