02745nas a2200313 4500008004100000022001400041245004600055210004300101260001500144300001600159490000700175520188000182653001302062653002102075653002602096653001502122653001702137653001702154653002602171653001902197653002802216100002402244700001902268700002702287700001802314700001702332700001502349856006702364 2020 eng d a0960-982200aA Tube-Dwelling Early Cambrian Lobopodian0 aTubeDwelling Early Cambrian Lobopodian c27/02/2020 a1529–15360 v303 a

Facivermis yunnanicus [1, 2] is an enigmatic worm-like animal from the early Cambrian Chengjiang Biota of Yunnan Province, China. It is a small (<10 cm) bilaterian with five pairs of spiny anterior arms, an elongated body, and a swollen posterior end. The unusual morphology of Facivermis has prompted a history of diverse taxonomic interpretations, including among annelids [1, 3], lophophorates [4], and pentastomids [5]. However, in other studies, Facivermis is considered to be more similar to lobopodians [2, 6, 7, 8]—the fossil grade from which modern panarthropods (arthropods, onychophorans, and tardigrades) are derived. In these studies, Facivermis is thought to be intermediate between cycloneuralian worms and lobopodians. Facivermis has therefore been suggested to represent an early endobenthic-epibenthic panarthropod transition [6] and to provide crucial insights into the origin of paired appendages [2]. However, the systematic affinity of Facivermis was poorly supported in a previous phylogeny [6], partially due to incomplete understanding of its morphology. Therefore, the evolutionary significance of Facivermis remains unresolved. In this study, we re-examine Facivermis from new material and the holotype, leading to the discovery of several new morphological features, such as paired eyes on the head and a dwelling tube. Comprehensive phylogenetic analyses using parsimony, Bayesian inference, and maximum likelihood all support Facivermis as a luolishaniid in a derived position within the onychophoran stem group rather than as a basal panarthropod. In contrast to previous studies, we therefore conclude that Facivermis provides a rare early Cambrian example of secondary loss to accommodate a highly specialized tube-dwelling lifestyle.

10aCambrian10aChengjiang Biota10aFacivermis yunnanicus10alobopodian10aluolishaniid10apanarthropod10aphylogenetic analyses10asecondary loss10atube-dwelling lifestyle1 aHoward, Richard, J.1 aHou, Xianguang1 aEdgecombe, Gregory, D.1 aSalge, Tobias1 aShi, Xiaomei1 aMa, Xiaoya uhttps://linkinghub.elsevier.com/retrieve/pii/S0960982220301196