Megadytes latus (Fabricius, 1801)

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 latus (Fabricius, 1801)

Figs 6 , 13 , 21 , 22 , 44-47 , 54 , 60 , 68

Dytiscus latus Fabricius, 1801: 260.

Trogus latus : Gemminger and Harold 1868:459.

Megadytes latus : Sharp 1882: 706; van den Branden 1885: 110; Chatanay 1910: 435; Bruch 1915: 478; Zimmermann 1919: 235; 1920: 256; Bruch 1927: 543; Guignot 1946: 118; Mouchamps 1957: 282; Trémouilles and Bachmann 1980: 108.

Cybister (Megadytes) latus : Wilke 1921: 248.

Megadytes lata : Blackwelder 1944: 80.

Megadytes (Megadytes) latus : Brinck 1945: 7.

Type locality.

South America.

Type specimens.

Syntypes in Zoological Museum der Universität Kiel, Germany, not examined.

Diagnosis.

This species differs from M. parvus in its larger size (TL = 19.5-23.2 mm in M. latus , Fig. 13 vs. TL = 13.0-14.6 mm in M. parvus , Fig. 12 ), broader shape (TL/GW = 1.7-1.8 in M. latus , Fig. 13 , vs. TL/GW = 1.9-2.1 in M. parvus , Fig. 12 ) as well as features of the male genitalia. In M. latus the male median lobe is relatively simple and evenly curved in lateral aspect with the apex narrowly rounded to somewhat pointed (Fig. 44 ). In M. parvus the median lobe is very broad in lateral aspect with the dorsal sclerite strongly expanded ventrally and curved with the apex strongly recurved (Fig. 39 ). The lateral lobe in M. latus is very slender apically (Fig. 44 ), but in M. parvus it is relatively broad throughout (Fig. 41 ).

Description.

Measurements. TL = 19.5-23.2 mm, GW = 11.4-13.4 mm, PW = 8.7-10.3 mm, HW = 5.3-6.2 mm, EW = 3.1-4.0 mm, TL/GW = 1.7-1.8, HW/EW = 1.6-1.7, WC/WV = 2.7-3.4. Body shape large and broadly oval, widest slightly posteriad of middle; lateral margins broadly curved, continuously curved between pronotum and elytron. Depressed and somewhat flattened in lateral aspect.

Coloration. Head dark green to dark brown, anteriorly somewhat green-rufous, clypeus pale rufous, labrum pale yellow. Pronotum dark green to dark brown, laterally broadly dark green-rufous. Elytron dark green with broad lateral green-rufous margins in some specimens. Ventral surfaces black, legs dark rufous.

Sculpture and structure. Head broad, anteriorly produced, eyes prominent; dorsal surface evenly covered with exceptionally fine microsculpture and dispersed micropunctures. Pronotum with lateral margins evenly and shallowly curved; surface of pronotum similar to surface of head in microsculpture and micropunctation; pronotum somewhat swollen anteriorly. Elytron with margins very broadly curved, more strongly curved posteriorly; surface similar to surface of head in microsculpture, but with extensive, very fine micropunctation over entire surface. Prosternal process anteriorly rounded, surface flat and moderately broad, apex broadly elongate and sharply pointed. Metaventral wing moderately broad, ~ 1/3 width of lateral portion of metacoxa; surface smooth, without sculpturing. Lateral portion of metacoxa large, broad, surface smooth, without sculpturing; metacoxal lines short and fine, extending anteriorly less than half distance across metacoxa. Abdominal ventrites smooth, unsculptured.

Male genitalia. Male median lobe in lateral aspect moderately slender throughout, evenly curved, apically narrowed, apex narrowly pointed (Fig. 44 ); in dorsal aspect moderately narrow, apically narrowed to narrowly rounded apex, ventral sclerite slender throughout length, apically abruptly expanded, apex rounded (Fig. 45 ). Lateral lobe slender throughout length, apically very slender, with long series of setae along dorsal margin (Fig. 46 ).

Female genitalia. The only female examined has the internal genitalia missing. Externally, the female gonocoxosternite is broad with the medial margin linear; the gonocoxae are together fused and knifelike, broad anteriorly, abruptly constricted subapically and apically linear to narrowly rounded apex (Fig. 60 ); rami short; other internal structures (vagina, spermatheca, etc.) not observed.

Sexual dimorphism. Males have a broad protarsal palette with ventral adhesive setae with apical structures in the form of elongate flattened structures; males also have mesotarsomeres with posteroventral fields of setae. Females lack natatory setae along the ventral margins of the metatarsomeres, but these are present in males. Males and females each have two metatarsal claws with the posterior shorter, but females have the posterior claw slightly longer than in the male (Figs 21 , 22 ).

Variation. Specimens exhibit variation in size (TL = 19.5-23.2 mm) but are consistent in shape (TL/GW = 1.7-1.8), and male genitalic shape and other features are relatively consistent across the range of the species. There is some variation in coloration with most specimens dark green-black, but a single specimen from the Gran Sabana, Venezuela (MIZA) is dorsally strikingly green. This specimen is also smaller than most (TL = 19.5 mm) and may represent a distinctive regional population or separate species.

Distribution.

This species is known from Argentina, Brazil, French Guiana, Uruguay ( Sharp 1882; Blackwelder 1944; Mouchamps 1957; Trémouilles and Bachmann 1980; Trémouilles 1989b), and Venezuela (MIZA, new country record).

Material examined.

Few specimens of this species exist in collections. Two specimens from Argentina, one from Bolivia (new country record), one from Brazil (KBMC), and a specimen from the Gran Sabana , Venezuela (MIZA) were examined for this study .

Figures

Figures 1 - 8. Cybistrinae morphological features 1 Bifurcitus lherminieri, right metatibia, posterior surface 2 Bifurcitus lherminieri, left metaleg, anterior surface 3 Trifurcitus robustus, left metaleg, anterior surface 4 Metaxydytes fraternus, left mesotarsomeres III-V, posterior surfaces 5 Cybister tripunctatus, left mesotarsomeres III-V, posterior surfaces 6 Megadytes latus, left half of metaventrite and left metacoxa (WV = metaventrite wing width, WC = metacoxal width) 7 Cybister tripunctatus, right metathoracic wing 8 Trifurcitus robustus, right metatrochanter, ventral surface. Scale bars: 1.0 mm.

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 51 - 57. Neotropical Cybistrinae species, male sternite IX, ventral aspect 51 Cybister festae 52 Cybister puncticollis 53 Nilssondytes diversus 54 Megadytes latus 55 Megadytes parvus 56 Paramegadytes glaucus 57 Metaxydytes fraternus. Scale bars: 1.0 mm.

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.

Figures 67 - 71. Third instar larva, anterior clypeal margin 67 Bifurcitus magnus 68 Megadytes latus 69 Metaxydytes carcharias 70 Paramegadytes glaucus 71 Trifurcitus fallax.