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Relationships among spider families that lack support through other lines of evidence (e.g., morphology) have recently been uncovered through molecular phylogenetics. One such group is the “marronoid” clade, which contains about 3,400 described species in 9 families. Marronoids run the gamut of life history strategies, with social species, species producing a variety of silk types, and species occurring in a range of extreme environments. Despite recognition of the ecological variability in the group, there remains uncertainty about family- level relationships, leaving diverse ecologies without an evolutionary context. The phylogenies produced to date have relatively low nodal support, there are few defined morphological synapomorphies, and the internal relationships of many families remain unclear. We use 93 exemplars from all marronoid families and ultraconserved element loci captured in silico from a combination of 48 novel low-coverage whole genomes and genomic data from the Sequence Read Archive (SRA) to produce a 50% occupancy matrix of 1,277 loci from a set of ultraconserved element probes. These loci were used to infer a phylogeny of the marronoid clade and to evaluate the familial relationships within the clade, and were combined with single-locus (Sanger) legacy data to further increase taxonomic sampling. Our results indicate a clearly defined and well-supported marronoid clade and provide evidence for both monophyly and paraphyly within the currently defined families of the clade. We propose taxonomic changes in accordance with the resulting phylogenetic hypothesis, including elevating Cicurinidae (restored status) and Macrobunidae (new rank).

Biodiversity catalogs are an invaluable resource for biological research. Efforts to scientifically document biodiversity have not been evenly applied, either because of charisma or because of ease of study. Spiders are among the most precisely cataloged and diverse invertebrates, having surpassed 50,000 described species globally. The World Spider Catalog presents a unique opportunity to assess the disproportionate documentation of spider diversity. In the present article, we develop a taxonomic ratio relating new species descriptions to other taxonomic activity as a proxy for taxonomic effort, using spiders as a case study. We use this taxonomic effort metric to examine biases along multiple axes: phylogeny, zoogeography, and socioeconomics. We also use this metric to estimate the number of species that remain to be described. This work informs arachnologists in identifying high-priority taxa and regions for species discovery and highlights the benefits of maintaining open-access taxonomic databases—a necessary step in overcoming bias and documenting the world's biodiversity.

Scorpions are an excellent system for understanding biogeographical patterns. Most major scorpion lineages predate modern landforms, making them suitable for testing hypotheses of vicariance and dispersal. The Caribbean islands are endowed with a rich and largely endemic scorpion fauna, the origins of which have not been previously investigated with modern biogeographical methods. Three sets of hypotheses have been proposed to explain present patterns of diversity in the Caribbean: (1) connections via land bridges, (2) vicariance events, and (3) overwater dispersal from continents and among islands. The present study investigates the biogeographical diversification of the New World buthid scorpion subfamily Centruroidinae Kraus, 1955, a clade of seven genera and more than 110 species; infers the ancestral distributions of these scorpions; and tests the relative roles of vicariance and dispersal in the formation of their present distributions. A fossil-calibrated molecular phylogeny was estimated with a Bayesian criterion to infer the dates of diversification events from which ancestral distributions were reconstructed, and the relative likelihood of models of vicariance vs. dispersal, calculated. Although both the timing of diversification and the ancestral distributions were congruent with the GAARlandia land-bridge hypothesis, there was no significant difference between distance-dependent models with or without the land-bridge.HeteroctenusPocock, 1893, the Caribbean-endemic sister taxon ofCentruroidesMarx, 1890 provides evidence for a Caribbean ancestor, which subsequently colonized Central America and North America, and eventually re-colonized the Greater Antilles. This ‘reverse colonization’ event of a continent from an island demonstrates the importance of islands as a potential source of biodiversity.