Rotundotergum Golovatch, Bouzan & Gallo, 2022

Golovatch, Sergei I., Bouzan, Rodrigo S., Gallo, Jéssica S. & Bichuette, Maria E., 2022, A new genus and two new species of the millipede family Chelodesmidae from Bahia state, northeastern Brazil, including a likely troglobiont (Diplopoda, Polydesmida), Zootaxa 5155 (1), pp. 87-104 : 98

Genus Rotundotergum Golovatch, Bouzan & Gallo , gen. nov.

Type species: Rotundotergum elevatum sp. nov., by present designation.

No other component species.

Name. To emphasize the very large and mostly regularly rounded mid-body paraterga, neutral in gender.

Diagnosis. A genus of Chelodesmidae that seems to be especially similar to both Eucampesmella Schubart, 1955 , with at least 12 species recognized, all in northern and northeastern Brazil, including Bahia ( Bouzan et al. 2021b), and Atlantodesmus Hoffman, 2000 , with at least six species distributed mostly along the Atlantic coast of Brazil, up to Bahia in the northeast ( Hoffman 2000; Bouzan et al. 2017, 2019). All their species are epigean, most show vivid colour patterns, and none has been encountered in caves. All three genera compared share, among other characters, the normal pore formula (5, 7, 9, 10, 12, 13, 15–19) and ozopores borne on distinct lateral calluses; the first few postcollum metaterga slightly broader than the following ones; very broad and laterally smooth paraterga; generally smooth metaterga devoid of a distinct transverse sulcus or impression; the presence of pleurosternal carinae; long and simple legs devoid of tibial chelae; a few small ridges traceable on a depressed caudal shelf of ovoid gonopodal apertures ( Fig. 9D ); sternal rudiments ( Fig. 10 , st) retained between enlarged gonocoxae (sometimes extended into apicolateral lobes to subtend the robust and untwisted gonopodal telopodites), but, above all, the same basic gonopodal conformation ( Figs 9D & 10 ), including the typical tripartite telopodite (Te), a usual, densely setose and relatively short prefemoral region (Pf) (relative to the acropodite); a prominent, long and fully independent, sometimes branching ( Eucampesmella ) prefemoral process (PfP); and a bifid acropodite (A) divided near midway into an often smaller and subspiniform solenomere (sl) and a more or less enlarged and sometimes complex end or side branch (= acropodital process, AP).

Rotundotergum gen. nov. differs from both Eucampesmella and Atlantodesmus in the mostly clearly upturned paraterga ( Fig. 8 ), vs. declivous, in Atlantodesmus also with angular, mostly sharpened caudal corners; the presence of a weak, but traceable transverse impression on most metaterga; the distinct and brush-like limbus ( Fig. 9B ), vs. smooth and even; the usual, not especially deep sulcus delimiting the gonopodal prefemoral region devoid of a cingulum distal to it ( Fig. 10 ), vs. strikingly deep in Eucampesmella ( Bouzan et al. 2021b) or, a little more distally, supplied with the so-called cingulum demarcating the basal region of the solenomere in Atlantodesmus ( Bouzan et al. 2017, 2019); and the prefemoral process unipartite, unciform, particularly strongly removed from, directed clearly caudomesad, and distally not attached to the acropodite ( Figs 9D & 10 ), vs. always suberect and closely attached to the acropodite at least distally ( Bouzan et al. 2017, 2019, 2021b).

Among both old genera compared above to Rotundotergum gen. nov., so far only Eucampesmella has been assigned to a tribe: Macrocoxodesmini Hoffman, 1990. This tribe is presently composed of only two genera, Macrocoxodesmus Schubart, 1947 and Eucampesmella , being characterized by the presence of trichosteles (= setigerous grains) on the male postfemora and tibiae, the hypertrophied valves of the vulvae, and the unusual curvature of the tracheal apodemes of female leg-pair 2 (Hoffman 1990; Bouzan et al. 2021b). Because these features fail to apply to Rotundotergum gen. nov., the new genus, like many other genera of Chelodesmidae , is bound to remain unassigned to a tribe yet.

Figures

FIGURE 8. Rotundotergum elevatum sp. nov., male paratype. A-C. Habitus, dorsal, lateral and ventral views, respectively. Photographs by K.V. Makarov, taken not to scale.

FIGURE 9. Rotundotergum elevatum sp. nov., male paratype. A. Incisura lateralis (I) beneath antenna, sublateral view. B. Body ring 7 with gonopods removed to show gonopod aperture, ventral view. C & D. Body ring 7 with intact gonopods, ventral and lateral views, respectively. Abbreviation: I, Incisura lateralis. Photographs by K.V. Makarov, taken not to scale.

FIGURE 10. Rotundotergum elevatum sp. nov., male paratype. A & B. Both gonopods, anterior and posterior views, respectively. C-F. Right gonopod, mesal, lateral, ventrocaudal and caudal views, respectively. Abbreviations: A, acropodite; c, cannula; Cx, gonocoxa; AP, acropodital process; lo, lateral lobe; Pf, prefemoral region; PfP, prefemoral process; sl, solenomere; st, sternal rudiment; Te, telopodite. Photographs by K.V. Makarov, taken not to scale.