Symphyla is one of the four major clades of Myriapoda (Myriapoda = Chilopoda [centipedes] + Diplopoda [millipedes] + Pauropoda [pauropods] + Symphala [symphylids]) (Rehm et al. 2014 and references therein). The centipedes, the only predatory myriapods, include around 5000 known species. The millipedes, which have two pairs of legs per segment, include around 12000 species. Pauropods and symphylids are small, translucent, soil-dwelling myriapods, with body lengths of less than 2 mm and 1 to 8 mm, respectively. The symphylids have long and filiform antennae and a pair of specialized appendages at the preanal segment known as spinnerets. The pauropods have distinctive antennae, which are branching and have long flagella. Around 800 pauropod species and around 200 symphylid species have been described (Minelli 2011).
A range of studies have inferred various different phylogenetic relationships among the four major myriapod groups. Dong et al. (2012) obtained the first complete mitochondrial genome sequence from a pauropod and, combining this in a phylogenetic analysis that included complete mitochondrial sequences from other myriapods, concluded that Pauropoda and Symphyla are sister groups. Miyazawa et al. (2014) reviewed various proposals, but based on their own molecular phylogenetic analysis they concluded that the symphylids are sister to the other three myriapod groups. This finding is consistent with the results of Rehm et al. (2014).
Dominguez Camacho (2010) undertook a morphology-based phylogenetic analysis of the Symphyla.
The Garden Symphylan (Scutigerella immaculata) is a significant crop pest in some areas (e.g., Umble and Fishher 2003 and references therein).
