Bäckstam , 2009 ( Araneae : Dipluridae ) is a junior synonym of Fufius Simon , 1888 ( Araneae : Cyrtaucheniidae )

The monotypic diplurid Metriura Drolshagen & Backstam, 2009 is placed in synonymy with Fufius (Cyrtaucheniidae) syn. nov. since Metriura lacks two of three diplurid synapomorphies (elongate posterior lateral spinnerets and the widely separated posterior median spinnerets) and shares synapomorphies with both aporoptychine cyrtaucheniids (subquadrate maxilla and a longer than wider labium) and Fufius (recurved and broad fovea, the typical incrassate tibia I of the male, with the spur having a single short branch and an apical megaspine, the basally curved metatarsus I and provided with a ventral tubercle). The type species of Metriura, M. striatipes Drolshagen & Backstam, 2009 is considered valid, and due to the synonymy of Metriura with Fufius, Fufius striatipes (Drolshagen & Backstam, 2009) comb. nov. is established.

explain their reasons for including their new genus in Dipluridae, but considered that Metriura belongs to Diplurinae because of the presence of two rows of teeth on the paired tarsal claws.They distinguished Metriura from Diplura, Trechona, and Harmonicon by the absence of a prolateral lyra on the maxillae, and from Linothele by the presence of a broader and longer labiosternal suture, two erect foveal setae in front of the fovea, a strongly curved base on metatarsus I, and a longer cymbium in males.They named the new genus "Metriura", which means "medium tail" in Greek, referring to the moderately long posterior lateral spinnerets.
The detailed original account of the male holotype of M. striatipes describes a specimen with two rows of teeth on superior tarsal claws, a long and slender embolus, a male spur with a single branch having an apical megaspine, a basally curved metatarsus I and a tubercle at the medial portion of the retroventral metatarsus I.These characteristics are compatible with diplurids but are not exclusive to the family.Conversely, the holotype has the labium longer than wider, subquadrate maxillae, and tarsi short and not pseudosegmented, which are not diplurinid characteristics (RAVEN 1985).Furthermore, the original description of M. striatipes does not include an illustration of the spinnerets, which are structures fundamental for assigning the species to the Dipluridae, since two of the three synapomophies of the family (RAVEN 1985) are related to these structures.Therefore, the inclusion of Metriura in Dipluridae is questionable and we herein reinterpret its taxonomic position.
In order to clarify the question, we reanalyzed the morphological characteristics provided in the description of M. striatipes based on voucher specimens and photographs of additional structures of the holotype.Specimens examined in this paper are deposited at the Instituto Nacional de Pesquisas da Amazônia, Manaus (INPA), at the Muséum national d'Histoire naturelle, Paris (MNHN), and the Museu Nacional, Rio de Janeiro (MNRJ).
Our study indicates that Metriura is not a diplurid because it lacks two of the three synapomorphies of the family; i.e., the posterior lateral spinnerets are not elongated and the posterior median spinnerets are not widely separated (Fig. 1).Moreover, the species resembles an aporoptychine cyrtaucheniid.Aporoptychines are characterized by a subquadrate maxilla, labium almost as long as wide or longer, a short diagonal fang, and the associated short fang groove (RAVEN 1985).A subquadrate maxilla and a labium that is longer than wide, two cyrtaucheniid characteristics, are clearly visible in the illustration of the holotype provided by DROLSHAGEN & BÄCKSTAM (2009).

Metriura
Other characteristics, such as a recurved and broad fovea, the typical incrassate tibia I of the male, with the spur having a single short branch and an apical megaspine, the basally curved metarsus I (RAVEN 1985) and provided with a ventral tubercle are all characteristics of species of Fufius Simon, 1888 (Cyrtaucheniidae Simon, 1889).In addition, the presence of "legs with distinct pattern consisting of 1-2 stripes on all segments except tarsi" (DROLSHAGEN & BÄCKSTAM 2009) in the juvenile paratype is also compatible with Fufius.The presence of this leg pattern is a common juvenile characteristic of many species of Fufius and may completely disappear when the specimen reaches maturity.All characteristics presented in the description, as well as those obtained by us, are compatible with the cyrtaucheniid Fufius.Therefore, the diplurid Metriura Drolshagen & Bäckstam, 2009 is here considered a junior synonym of the cyrtaucheniid Fufius Simon, 1888 syn.nov.; and, consequently, M. striatipes is transferred to Fufius striatipes (Drolshagen & Bäckstam 2009) comb.nov.. Examination of most of the holotypes of the known species of Fufius indicates that F. striatipes is a valid species.