Millipede phylogeny revisited in the light of the enigmatic order Siphoniulida

The discovery of six specimens of the enigmatic order Siphoniulida, including for the first time males, prompted a modern re-analysis of current phylogenetic schemes for the class Diplopoda derived from traditional morphological and developmental characters. The data matrix was constructed and analysed using paup. The resulting phylogenetic hypotheses corroborated the longest standing, traditional classification, but also demonstrated clearly that more characters must be included to reach a better resolution. Recent alternative phylogenetic hypotheses and classifications are discussed in the light of the current analysis. The validity of a putative helminthomorph synapomorphy, the location of male gonopods on the 7th body ring, is discussed. Scanning electron microscopy corroborated morphological characters already described for the Siphoniulida: modified anterior legs, an apparently legless 3rd body ring, pyriform head, antennae with clavate setae, and absence of ozopores. The highly modified gonopods of the Siphoniulida are described for the first time; only the anterior legs of the 7th ring are modified into gonopods, the posterior legs of this ring are developed as normal walking legs. The gnathochilarium differs from the Colobognatha and consists of well-developed stipites with palps, elongated lingual plates with palps and a narrow central sclerite, most likely the mentum. Structures on the epiproct may possibly be spinnerets. Despite the discovery of adult males, the Siphoniulida are still considered Helminthomorpha incertae sedis.