Hexurellidae

Distinguished from other atypoid families by extremely small adult size (2.5–5 mm), the smallest among mygalomorph spiders. As mygalomorphs, possess two pairs of book lungs and parallel cheliceral fangs. The family can be differentiated from Hexuridae and other atypoids by phylogenomic placement as sister to all remaining atypoids. Species-level identification within Hexurella requires examination of genitalia and other morphological features described in recent taxonomic revisions.

Montane habitats including sky islands of southern Arizona and northern Mexico; sclerophyllous woody plant communities; cryptic microhabitats under rocks and in leaf litter. Occupies upland habitats of southern California, Baja California Norte, central and southeastern Arizona, the Mojave Desert of California, and mountains of northwest Arizona. Populations occur in disjunct mountain ranges isolated by arid lowland basins.

United States-Mexico borderlands: central and southeastern montane Arizona, southern California, northern Baja California Norte, northwestern Arizona. Range extends south into Baja California Norte and north into the Mojave Desert of California. Additional species are predicted in mountains of central and northwestern Arizona, northern mainland Mexico, and the Mojave Desert of California.

Vagrant and web-building with cryptic natural history. Exhibits strict microhabitat preferences and potentially poor dispersal capabilities. Has been observed in association with Sitalcina harvesters (Opiliones) at some locations.

• HexuridaeFormerly included Hexurella; distinguished by phylogenomic placement and retained as separate family containing larger-bodied genera
• Other Atypoidea families (Antrodiaetidae, Actinopodidae, etc.)Hexurellidae is sister to all remaining atypoids; other families share mygalomorph traits but are phylogenetically more derived and generally larger-bodied

• mygalomorph
• atypoid
• relictual
• sky island
• micro-endemic
• US-Mexico borderlands
• phylogenomics
• dwarf spiders

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• Catalogue of Life
• Gotta Love Those Spiders | Bug Squad
• Species delimitation, biogeography, and natural history of dwarf funnel web spiders (Mygalomorphae, Hexurellidae, Hexurella) from the United States / Mexico borderlands.