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Higher-level classifications often must account for monotypic taxa representing depauperate evolutionary lineages and lacking synapomorphies of their better-known, well-defined sister clades. In a ranked (Linnean) or unranked (phylogenetic) classification system, discovering such a depauperate taxon does not necessarily invalidate the rank classification of sister clades. Named higher taxa must be monophyletic to be phylogenetically valid. Ranked taxa above the species level should also maximize information content, diagnosability, and utility (e.g., in biodiversity conservation). In spider classification, families are the highest rank that is systematically catalogued, and incertae sedis is not allowed. Consequently, it is important that family-level taxa be well defined and informative. We revisit the classification problem of Orbipurae, an unranked suprafamilial clade containing the spider families Nephilidae, Phonognathidae, and Araneidae sensu stricto. We argue that, to maximize diagnosability, information content, conservation utility, and practical taxonomic considerations, this “splitting” scheme is superior to its recently proposed alternative, which lumps these families together as Araneidae sensu lato. We propose to redefine Araneidae and recognize a monogeneric spider family, Paraplectanoididae fam. nov. to accommodate the depauperate lineage Paraplectanoides. We present new subgenomic data to stabilize Orbipurae topology which also supports our proposed family-level classification. Our example from spiders demonstrates why classifications must be able to accommodate depauperate evolutionary lineages, for example, Paraplectanoides. Finally, although clade age should not be a criterion to determine rank, other things being equal, comparable ages of similarly ranked taxa do benefit comparative biology. [Classification, family rank, phylogenomics, systematics, monophyly, spider phylogeny.]

Island systems provide excellent arenas to test evolutionary hypotheses pertaining to gene flow and diversification of dispersal-limited organisms. Here we focus on an orbweaver spider genusCyrtognatha(Tetragnathidae) from the Caribbean, with the aims to reconstruct its evolutionary history, examine its biogeographic history in the archipelago, and to estimate the timing and route of Caribbean colonization. Specifically, we test ifCyrtognathabiogeographic history is consistent with an ancient vicariant scenario (the GAARlandia landbridge hypothesis) or overwater dispersal. We reconstructed a species level phylogeny based on one mitochondrial (COI) and one nuclear (28S) marker. We then used this topology to constrain a time-calibrated mtDNA phylogeny, for subsequent biogeographical analyses in BioGeoBEARS of over 100 originally sampledCyrtognathaindividuals, using models with and without a founder event parameter. Our results suggest a radiation of CaribbeanCyrtognatha, containing 11 to 14 species that are exclusively single island endemics. Although biogeographic reconstructions cannot refute a vicariant origin of the Caribbean clade, possibly an artifact of sparse outgroup availability, they indicate timing of colonization that is much too recent for GAARlandia to have played a role. Instead, an overwater colonization to the Caribbean in mid-Miocene better explains the data. From Hispaniola,Cyrtognathasubsequently dispersed to, and diversified on, the other islands of the Greater, and Lesser Antilles. Within the constraints of our island system and data, a model that omits the founder event parameter from biogeographic analysis is less suitable than the equivalent model with a founder event.

The Caribbean archipelago offers one of the best natural arenas for testing biogeographic hypotheses. The intermediate dispersal model of biogeography (IDM) predicts variation in species richness among lineages on islands to relate to their dispersal potential. To test this model, one would need background knowledge of dispersal potential of lineages and their biogeographic patterns, which has been problematic as evidenced by our prior work on the Caribbean tetragnathid spiders. In order to investigate the biogeographic imprint of an excellent disperser, we studyTrichonephilain the Americas.Trichonephilais a nephilid genus that contains globally distributed species known to overcome long, overwater distances. The results of our phylogenetic and population genetic analyses onT. clavipessuggest that populations over the Caribbean and North America maintain a lively gene flow. However, the single species status ofT. clavipesover the entire New World is challenged by our species delimitation analyses. Combined with prior evidence from spider genera of different dispersal ability, these patterns coming from an excellent disperser (Trichonephila) that is species‐poor and of a relatively homogenous genetic structure, support the IDM predictions.