Fontidessus Miller and Spangler

Fontidessus Miller and Spangler, new genus

(Figs 1–17)

Type species. Fontidessus toboganensis Miller, new species by current designation.

Diagnosis and description. Fontidessus is clearly a member of the tribe Bidessini based on the bi-segmented lateral lobes of the aedeagus (Figs 10, 13, 16) (Biström, 1988) and the presence of a distinct spermathecal spine (Fig. 17) (Miller, 2001). Fontidessus differs from other genera in the tribe by the combination of: 1) transverse occipital line absent (Figs 1–3), 2) basal pronotal striae present (Figs 1–3), 3) basal elytral stria absent (Figs 1–3), 4) elytral sutural stria faintly present in some specimens (e.g. Fig. 1), 5) anterior clypeal margin unmodified, 6) elytron without longitudinal carinae, 7) epipleuron without transverse carina at humeral angle, 8) lateral lobes of aedeagus two-segmented (Figs 10, 13, 16), 9) habitus elongate, oval, with lateral pronotal and elytral margins nearly continuously and shallowly curved (Figs 1–3), and 10) metatrochanter extremely large relative to metafemur, approximately 0.6 × length of metafemur (Fig. 4).

This genus is most similar to the genera Uvarus Guignot and Bidessodes Régimbart (to which it keys in Biström’s 1988 key to bidessine genera). From Bidessodes it differs by 1) dorsum not iridescent, and 2) metatibiae without natatory setae and metatarsi with few natatory setae. Bidessodes appears to be a monophyletic group. Although some of its members have dramatic modifications to the male legs or genitalia, they are superficially quite similar and have similar iridescence and color pattern on the dorsal surface. Fontidessus specimens lack these features. Despite the absence of a cladistic phylogenetic analysis, Fontidessus appears to be clearly outside Bidessodes.

From Uvarus, Fontidessus genus differs in lacking basal elytra striae and natatory setae. It is, however, quite similar to Uvarus genus in most characters and general features such as shape, size and coloration. The problem with these observations is that Uvarus is a heterogeneous group with a worldwide distribution. Within Bidessini it is the “trashcan” group that includes those taxa without an occipital line but also without any unifying synapomorphy. Placing these new species in Uvarus would require an expansion of an already problematic group to include a new character combination. It seems more desirable to place these species in a new genus until the classification of the Bidessini can be more thoroughly tested (see Discussion below).

Etymology. This genus is named Fontidessus from the Latin word fontis, meaning “spring,” referring to the seepage-like habitat of the type locality of the type species, and dessus, a common root for genus names in the tribe Bidessini

Distribution and habitat. The genus is known from three sympatric species from only a single site in Venezuela (see type localities below). In each case, however, the species do not appear to occupy typical open water. Instead they appear to occur in seeps or shallow water at stream margins.

Discussion. The genera of Bidessini are currently defined based on the combination of several characters such as the presence or absent of an occipital line, basal sutural and pronotal striae, epipleural carinae, elytra carinae and more subjective characters such as general shape. Because of the nature of the various combinations it is clear that homoplasy, or loss, is exhibited in many of the characters throughout the tribe. There has been only limited cladistic testing of these characters (e.g. Miller et al., 2006). When new species are discovered with a new combination of characters, such as those described here, it is not easy to decide whether to erect a new genus or expand the definition of existing genera (which may require synonymy with other genera). It seems best, in the absence of cladistic testing of relationships and putative homologies, to place anomalous species in new genera to draw attention to their unique character combination until such time as the genera can be phylogenetically revised. In further support of the placement of this taxon outside both Uvarus and Bidessodes, a recent molecular phylogenetic analysis of Dytiscidae by Ribera et al. (2008) included at least one member of this new genus. According to M. Balke (personal communication), “ unknown Bidessini a ” in that analysis (MB1171, Ribera et al., 2008) is the species described here as F. toboganensis. In their analysis F. toboganensis is resolved with two other unidentified Bidessini and well removed from either Uvarus or Bidessodes (Ribera et al., 2008).