Tuoba Chamberlin 1920

Genus Tuoba Chamberlin, 1920 Hovanyx Lawrence, 1960, syn. nov. Mixophilus Silvestri, 1929 syn. nov. Remarks. The monotypic genus Mixophilus was erected by Silvestri (1929) to place a new species of geophilomorph sampled from riparian sites in Madras (Chennai), Southern India. The original description of Mixophilus indicus includes illustrations of the head, forcipular apparatus and ultimate leg-bearing segment as well as detailed ecological observations concerning its preferred microhabitats in the type locality. Subsequent physiological investigations revealed a modified tracheal system, comprising possible adaptations to immersion for long periods of time (Rajulu 1970). An affinity to Henia and Chaetechelyne (Dignathodontidae) was suggested, however, within the same section Silvestri (1929) pointed to differences between Mixophilus and both of these genera in “ the structure of the labrum ” (tripartite in M. indicus but unipartite in Dignathodontidae), “ the distribution of sternal pores ” (transverse band in M. indicus, medial sub-circular / elliptical field in Dignathodontidae), in the last leg-bearing segment (telopodite composed of 7 articles in M. indicus but 6 in Henia), and in the elongation of the forcipular pretergite (longer in M. indicus than in Chaetechelyne). The structure of the labrum described and illustrated for M. indicus, comprising three conspicuous pieces, suggests a close affinity to other members of Geophilidae s. str. An estuarine habitat preference and multiple morphological characters show a near complete overlap between the diagnoses of Tuoba and Mixophilus (Table 3). Complete chitin lines in M. indicus may indicate intraspecific or interspecific variability which has been recorded in Tuoba (Jones 1998) or artifacts of examination under light microscopy. In light of this re-evaluation of its original description, we propose reassignment of M. indicus to Tuoba considering the available data on its morphology, with Tuoba indica comb. nov. as the valid name for specimens on which its original description was based. Consequently, we propose that Mixophilus is the junior subjective synonym of Tuoba syn. nov. Similarities between Tuoba indica comb. nov. and T. sydneyensis exist in elongation of the ultimate legs and reduction of the second maxillary pretarsus, however these characters are shared by several species of Tuoba. The incomplete original description provided by Silvestri does not allow for definitive assignment of Tuoba indica comb. nov. to another species of Tuoba until the type material can be adequately re-described. Similarly, the genus Hovanyx was erected for the species Hovanyx waterloti, described in Lawrence’s (1960) catalogue of Malagasy centipedes. An affinity to Dignathodontidae was again proposed based on similarities in the structure of the labrum, originally described for H. waterloti as composed of a single piece and bearing a small number of rudimentary, anteriorly oriented tubercles (“ Labre […] à dents pas très distinctes, quatre courtes dents triangulaires dirigées vers l’avant, de chaque côté. ”). The diagnosis of Hovanyx singled out the absence of coxal organs (“ […] diffère de tous les autres membres de la sous-famille des Dignathodontinæ par l’absence de pores aux pattes terminales. ”) as the main distinguishing trait separating it from all other dignathodontid genera. However, both the original description and accompanying illustrations suggest a closer affinity to Geophilidae s. str., as multiple other morphological characters (shape of head, forcipular coxosternite, metasternal pore fields) are characteristic of the Geophilidae rather than the Dignathodontidae, and subsequent taxonomic revision of both families placed Hovanyx under Geophilidae (Bonato 2011). Furthermore, the incomplete original description overlaps almost entirely with that of T. sydneyensis, a wide-ranging geophilid encountered in littoral sites in the Seychelles (Bonato and Minelli 2010) and the Aldabra Atoll (present records) close to the type locality of H. waterloti. Shared characters include range of leg bearing segment number (41–43), morphology of the labrum, condition of chitin lines on the forcipular coxosternite (incomplete) (Table 3). The only putative differences between H. waterloti and T. sydneyensis are the unipartite labrum and absence of coxal organs in the former (Table 3). These may however be unreliable characters because of inadequate documentation, as published illustrations of Tuoba specimens and the material here illustrated show great variability in the orientation and shape of the labral pieces, which depending on the degree of sclerotization seen in the specimen and shape and number of denticles on the side pieces, may resemble the labrum of Dignathodontidae under light microscopy. The absence of coxal organs has not been previously reported in any species of Tuoba, however this character shows extensive ontogenetic plasticity within Geophilidae (Horneland and Meidell 2009; Gregory and Barber 2010; Tuf and Dányi 2015; Peretti and Bonato 2016; Stojanović et al. 2020) and the small size of the holotype and only known specimen as well as variations in clearing and position of the coxopleuron may render the pit inconspicuous.