Megadytes species" Ribera et al. 2008

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

" Megadytes species" Ribera et al. 2008

Figs 14 , 25 , 48-50

Megadytes species IR57: Ribera et al. 2008: 25.

Discussion.

This single male specimen of a cybistrine from Peru presents some problems. It appears to be an undescribed species based on the male genitalia (Figs 48-50 ). The specimen was DNA sequenced and analyzed for a project by Ribera et al. (2008) where it was found to be in a group with species then Megadytes assigned to Megadytes (including species of M. (Bifurcitus) , M. (Paramegadytes) and M. (Megadytes) ). The male specimen currently includes a single metathoracic leg (the other is absent). On it, there are two unequal length metatarsal claws with the posterior short, much shorter than the anterior (Fig. 25 ), which places it outside the historical diagnosis of Megadytes which includes males with equal-length metatarsal claws (although see above). However, the specimen is missing important morphological structures for further interpreting its placement within Cybistrinae including the mesothoracic legs (which are important for examining the posterodorsal series of setae on the mesotarsomeres) and components of the genital capsule (which are important for examining the emargination of the medial margins of abdominal sternite IX). Because of this, the specimen cannot be placed within a known genus. Nor is it reasonable to place it in a new genus or expand the definition of an existing genus to include it given the lack of information about its features. Hopefully, additional specimens will be found to allow this species to be described and placed. The species is described here to the extent possible to allow for future identification and investigation.

Collection locality.

Peru, Atalapa, Rio Carbon at Rio Madre de Dios, in river, Apr 1999 ( Ribera et al. 2008).

Description.

Measurements. TL = 17.5 mm, GW = 10.4 mm, PW = 12.8 mm, HW = 4.8 mm, EW = 2.4 mm, TL/GW = 1.7, HW/EW = 2.0, WC/WV = 4.2. Body shape (Fig. 14 ) broad, expanded posteriorly, widest at ~ 3/5 of length; lateral margins evenly, continuously curved between pronotum and elytron. Depressed and somewhat flattened in lateral aspect.

Coloration. All dorsal surfaces dark reddish brown, without yellow margins on pronotum or elytron. Ventral surfaces entirely dark reddish brown, somewhat more reddish on ventral surfaces of prothorax and pro- and mesothoracic legs.

Sculpture and structure. Head broad; anterior clypeal margin broadly, shallowly and evenly concave; eyes large (HW/EW = 2.0). Dorsal surface shiny and evenly covered with fine micropunctures on head and pronotum, very few sparse micropunctures on elytron. Pronotum with lateral margins evenly and broadly curved. Elytral lateral margin evenly and slightly curved for most of length, apically broadly curved. Prosternal process apically broadly, shallowly concave, ventral surface flat throughout, apex robust, acutely pointed. Metaventral wing narrow, ~ 1/4 width of lateral portion of metacoxa (WC/WV = 4.2); surface smooth, with extremely fine punctation. Lateral portion of metacoxa large, broad, surface smooth, with dispersed, very fine micropunctures; metacoxal lines short, extending only ~ 1/3 distance across metacoxa. Abdominal ventrites smooth, unsculptured.

Male genitalia. Male median lobe in lateral aspect slender, broader submedially and gradually narrowed apically to slightly curved apex, apex bluntly rounded (Fig. 48 ). In dorsal aspect slender, evenly and gradually narrowed to narrowly rounded apex; dorsal sclerite very slender and elongate (Fig. 49 ). Lateral lobe extremely slender throughout, broadly curved with long series of long setae along dorsal margin (Fig. 50 ).

Female genitalia. Females are not known.

Sexual dimorphism. Only a single male was examined. However, this male has a characteristic broad protarsal palette with ventral adhesive setae. Males also have mesotarsomeres with clumps of posteroventral setae. Other typical sexually dimorphic features cannot be compared.

Variation. Only a single specimen was examined.

Material examined.

A single male specimen examined labeled, "271297 PERU ZUNGARO COHA 16u:TO [handwritten, somewhat illegible]."

Figures

Figures 9 - 14. Neotropical Cybistrinae species, habitus 9 Cybister festae 10 Cybister puncticollis 11 Nilssondytes diversus 12 Megadytes parvus 13 Megadytes latus 14 species " IR 57 " (Ribera et al. 2008). Scale bar: 10.0 mm.

Figures 15 - 29. Neotropical Cybistrinae species, metatarsal claws and tarsomere VI of males and females 15, 16 Cybister festae 17, 18 Cybister puncticollis 19, 20 Nilssondytes diversus 21, 22 Megadytes latus 23, 24 Megadytes parvus 25 species " IR 57 " (Ribera et al. 2008) 26, 27 Paramegadytes glaucus 28, 29 Metaxydytes fraternus. Scale bars: 1.0 mm.

Figures 30 - 50. Neotropical Cybistrinae species, male genitalia 30 - 32 Cybister festae: 30 median lobe, right lateral aspect 31 median lobe, ventral aspect 32 right lateral lobe, right lateral aspect 33 - 35 Cybister puncticollis: 33 median lobe, right lateral aspect 34 median lobe, ventral aspect 35 right lateral lobe, right lateral aspect 36 - 38 Nilssondytes diversus: 36 median lobe, right lateral aspect 37 median lobe, ventral aspect 38 right lateral lobe, right lateral aspect 39 - 43 Megadytes parvus: 39 median lobe, right lateral aspect 40 median lobe, ventral aspect 41 right lateral lobe, right lateral aspect 42 apex of median lobe, right lateral aspect 43 apex of median lobe, ventral aspect 44 - 47 Megadytes latus: 44 median lobe, right lateral aspect 45 median lobe, ventral aspect 46 right lateral lobe, right lateral aspect 47 apex of median lobe, ventral aspect 48 - 50 species " IR 57 " (Ribera et al. 2008): 48 median lobe, right lateral aspect 49 median lobe, ventral aspect 50 right lateral lobe, right lateral aspect.

Figures 58 - 61. Neotropical Cybistrinae species, female genitalia including left gonocoxosternite, ventral aspect, except Fig. 60 without internal genitalia 58 Cybister festae 59 Cybister puncticollis 60 Megadytes latus 61 Nilssondytes diversus. Scale bars: 1.0 mm.