Megadytes Sharp, 1882

Figs 6, 12, 13, 21-24, 39-47, 54, 55, 60, 68

Megadytes Sharp, 1882: 701.

Type species.

Megadytes latus Fabricius, 1801: 260.

Classification.

The concept of the genus presented here differs significantly from previous ones (e.g., Trémouilles and Bachmann 1980; Miller et al. 2007; Miller and Bergsten 2016). The type species of Megadytes is M. latus Fabricius, 1801, a species which differs in important phylogenetic characters from most other species historically Megadytes assigned to Megadytes . Here the species M. latus is placed together with Megadytes parvus comb. nov. in Megadytes, whereas the other species historically in Megadytes are placed in other genera based on the phylogenetic hypothesis developed here (Figs 75, 76). Given the character distribution in this group and the diagnosis of the type species, M. latus, this new classification is unavoidably disruptive of the historical concept of the genus (which included all species here placed in the genera Bifurcitus stat. nov., Paramegadytes new status, and Trifurcitus new status, see below) and a new genus described below. The unusual characteristics of M. parvus were recognized by Trémouilles (1984) who placed the species in Cybister (Meganectes) Brinck, 1945.

Diagnosis.

Within Cybistrinae Megadytes are similar to Cybister (Figs 51, 52) in having the medial margin of the lobes of the male abdominal sternum IX emarginate (Figs 54, 55), but differ from Cybister (Fig. 5) in lacking a series of setae along the posterodorsal apical angle of the mesotarsomeres of males and pro- and mesotarsomeres of females (as in Fig. 4) This places them in an intermediate phylogenetic position between other Cybistrinae and Cybister (Figs 75, 76, see below). Males and females both have two metatarsal claws with the posterior claw strongly reduced (Figs 21-24). Third instar larvae (based on M. latus) have (1) the median lobe of the frontoclypeus truncate apically with a tuft of setae, (2) the median and lateral lobes of the frontoclypeus separated by a wide emargination (Fig. 68), (3) the lateral lobes of the frontoclypeus apically simple (Fig. 68), (4) the lateral lobes of the frontoclypeus acutely angulate (Fig. 68), and (5) the cephalic capsule relatively long (head length / head width> 1.25).

Distribution.

Megadytes are found in the Neotropical region. Megadytes parvus is known only from the type locality in Bahia State, Brazil, and M. latus is known from Brazil, Uruguay, Argentina, French Guiana, and Venezuela.

Phylogenetic relationships.

Megadytes is sister to Cybister (Figs 75, 76) based on both genera with distinctly emarginate medial margins of abdominal sternite IX in males (Figs 51-55). However, Megadytes lack a series of setae at the apicodorsal angle of the posterior surface of mesotarsomeres I-IV (and of protarsomeres I-IV of females). This feature is remarkably consistent across the numerous Cybister species in the world (Miller et al. 2007).