Megadytes Sharp, 1882

Miller, Kelly B., Michat, Mariano C. & Ferreira Jr, Nelson, 2024, Reclassification of Cybistrinae Sharp, 1880 in the Neotropical Region (Coleoptera, Adephaga, Dytiscidae), with description of new taxa, ZooKeys 1188, pp. 125-168 : 125

publication ID

https://dx.doi.org/10.3897/zookeys.1188.110081

publication LSID

lsid:zoobank.org:pub:997ADB92-AFA7-4979-82A2-B81C00EF3AEA

persistent identifier

https://treatment.plazi.org/id/8F1795AC-ACC0-5B4F-A5C5-0BA82BD97C67

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ZooKeys by Pensoft

scientific name

Megadytes Sharp, 1882
status

 

Megadytes Sharp, 1882 View in CoL

Figs 6 View Figures 1–8 , 12 View Figures 9–14 , 13 View Figures 9–14 , 21-24 View Figures 15–29 , 39-47 View Figures 30–50 , 54 View Figures 51–57 , 55 View Figures 51–57 , 60 View Figures 58–61 , 68 View Figures 67–71

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 View Figure 75 , 76 View Figure 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 View Figures 51–57 , 52 View Figures 51–57 ) in having the medial margin of the lobes of the male abdominal sternum IX emarginate (Figs 54 View Figures 51–57 , 55 View Figures 51–57 ), but differ from Cybister (Fig. 5 View Figures 1–8 ) 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 View Figures 1–8 ) This places them in an intermediate phylogenetic position between other Cybistrinae and Cybister (Figs 75 View Figure 75 , 76 View Figure 76 , see below). Males and females both have two metatarsal claws with the posterior claw strongly reduced (Figs 21-24 View Figures 15–29 ). 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 View Figures 67–71 ), (3) the lateral lobes of the frontoclypeus apically simple (Fig. 68 View Figures 67–71 ), (4) the lateral lobes of the frontoclypeus acutely angulate (Fig. 68 View Figures 67–71 ), 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 View Figure 75 , 76 View Figure 76 ) based on both genera with distinctly emarginate medial margins of abdominal sternite IX in males (Figs 51-55 View Figures 51–57 ). 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).

Kingdom

Animalia

Phylum

Arthropoda

Class

Insecta

Order

Coleoptera

Family

Dytiscidae

Loc

Megadytes Sharp, 1882

Miller, Kelly B., Michat, Mariano C. & Ferreira Jr, Nelson 2024
2024
Loc

Megadytes

Sharp 1882
1882