Solving a running crab spider puzzle: delimiting Cleocnemis Simon, 1886 with implications on the phylogeny and terminology of genital structures of Philodromidae

BACKGROUND: Among the 16 Neotropical genera of Philodromidae, Cleocnemis has the most troublesome taxonomic situation. Remarkable morphological differences among several genera historically said to be related to Cleocnemis denote controversial notions and general uncertainty about the genus identity. Thus, to clarify the genus limits and contribute to the understanding of Neotropical Philodromidae, we conducted a morphological analysis, along with Bayesian Inference and Maximum Likelihood molecular phylogenetic analyses focusing on Cleocnemis and related genera of Thanatinae. All of the 14 species previously placed in Cleocnemis were studied, and eight of them included in the molecular analyses based on fragments of 28S rDNA, histone H3, 16S rDNA, and cytochrome oxidase I (COI). RESULTS: Cleocnemis was recovered as polyphyletic. Most of its species are distributed into six lineages allocated into five morphologically recognizable groups: Group I [Cleocnemis heteropoda], representing Cleocnemis sensu stricto and two new junior synonyms, Berlandiella and Metacleocnemis; Group II [Tibelloides bryantae comb. nov., Tibelloides punctulatus comb. nov., Tibelloides reimoseri nom. nov., and Tibelloides taquarae comb. nov.], representing Tibelloides gen. rev., which was not recovered as monophyletic; Group III [Fageia moschata comb. nov., Fageia rosea comb. nov.], representing the genus Fageia; Group IV [“Cleocnemis” lanceolata]; and Group V [“Cleocnemis” mutilata, “Cleocnemis” serrana, and “Cleocnemis” xenotypa]. Species of the latter two groups are considered incertae sedis. Cleocnemis spinosa is maintained in Cleocnemis, but considered a nomen dubium. Cleocnemis nigra is considered both nomen dubium and incertae sedis. We provide a redelimitation of Cleocnemis, redescription, neotype designation, and synonymy of type-species C. heteropoda. Taxonomic notes on composition, diagnosis, and distribution for each cited genus are also provided. Phylogenetic results support the division of Philodromidae into Thanatinae new stat. and Philodrominae new stat. and suggest expansion of their current compositions. Terminology of genital structures of Philodromidae is discussed. CONCLUSIONS: Our results bring light to Cleocnemis taxonomy and enhance the understanding of the relationships within Philodromidae, especially through the assessment of neglected Neotropical taxa. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40850-022-00136-7.