Since studies based on morphological characters have failed to give a satisfactory answer, a broad scale molecular study is under way ((Nardi et al., 2001), Frati et al, submitted, il Gomphiocephalus) in order to use mitochondrial genome sequences to study the evolution and differentiation of the most basal hexapod groups, including Tricholepidion. If the latter hypothesis proved to be true, the family Lepidotrichidae, would better deserve the ordinal rank. Tricholepidion (and therefore the whole family Lepidotrichidae) has been considered either as belonging to the order Zygentoma (Kristensen, 1997 Wygodzinsky, 1961), or basal to the rest of the Zygentoma plus the Pterygota (Beutel, 2001 Bitsch and Bitsch, more ยป 2000 Staniczek, 2000), although the significance of some of the morphological characters on which these analyses are based have been questioned (Dallai et al., 2001 Kristensen, 1997). Since this species was first described (Wygodzinsky, 1961) its phylogenetic position has been difficult to establish, due to an 'array of unique characters' that are difficult to interpret in a phylogenetic framework. The only living representative of this family is Tricholepidion gertschi Wygodzinski. The family Lepidotrichidae was first described by (Silvestri, 1912) (1912: 'Lepidothricinae') from a Baltic Amber fossil (Lepidothrix pilifera Menge). In fact, these relationships constitute one of the most debated issues in hexapod phylogeny. Further, within these groups are hotly debated issues, including the monophyly of Entognata (Koch, 1997 Kukalova Peck, 1987), the monophyly of Diplura (Bilinski, 1993 Stys and Bilinski, 1990), the affinity between Collembola and Protura (Dallai, 1994 Kristensen, 1981) and the position of Lepidotrichidae (below). ![]() However, some studies have questioned this affinity with insects (Dallai, Abele, Spears, Nardi). Traditionally, the 'Apterygota' has been thought to consist of five orders of wingless hexapods (Protura, Collembola, Diplura, Microcoryphia and Zygentoma) believed to be collectively basal to insects (i.e., the Pterygota).
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