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Improving family-level classifications

Named higher taxa, for example genera and families, must be monophyletic to be phylogenetically valid. Ranked taxa above the species level should also maximize information content, diagnosability, and utility. Often, higher-level classifications must account for monotypic taxa representing depauperate evolutionary lineages and lacking synapomorphies of their better-known, well-defined sister clades. Discovering such a depauperate taxon does not necessarily invalidate the rank classification of sister clades.

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. Here, we revisit the classification problem of Orbipurae, an unranked suprafamilial clade containing the spider families Nephilidae, Phonognathidae, and Araneidae sensu stricto, as well as the "rogue" monotypic genus Paraplectanoides.

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. Our example from spiders demonstrates why classifications must be able to accommodate depauperate evolutionary lineages, e.g., Paraplectanoides.


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