Research Article |
Corresponding author: Kelly B. Miller ( kbmiller@unm.edu ) Academic editor: Michael Ivie
© 2024 Kelly B. Miller, Mariano C. Michat, Nelson Ferreira Jr.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Miller KB, Michat MC, Ferreira Jr N (2024) Reclassification of Cybistrinae Sharp, 1880 in the Neotropical Region (Coleoptera, Adephaga, Dytiscidae), with description of new taxa. ZooKeys 1188: 125-168. https://doi.org/10.3897/zookeys.1188.110081
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The classification of the Neotropical Cybistrinae Sharp, 1880 (Coleoptera: Adephaga: Dytiscidae) is extensively revised based on a phylogenetic analysis of morphological features of the group. A new genus, Nilssondytes gen. nov. is described for a unique new species, Nilssondytes diversus sp. nov. from Venezuela. The New World genus, Megadytes Sharp, 1882, with several subgenera, was found to not be monophyletic. The type species of Megadytes, Dytiscus latus Fabricius, 1801 and the species Cybister parvus Trémouilles, 1984 were found to be monophyletic together, and phylogenetically more closely related to Cybister Curtis, 1827 than to other species assigned to Megadytes sensu stricto, which were found to also be monophyletic. The name Megadytes is here restricted to include only Megadytes latus and Megadytes parvus. These two species assigned to this newly restricted genus concept are reviewed and diagnosed. A new genus, Metaxydytes gen. nov., is erected to include all the other species currently assigned to Megadytes sensu stricto. The current subgenus names assigned to Megadytes, Bifurcitus Brinck, 1945, Paramegadytes Trémouilles & Bachmann, 1980, and Trifurcitus Brinck, 1945, are elevated to genus rank since they are variously paraphyletic. The two species assigned to Cybister (Neocybister) Miller, Bergsten & Whiting, 2007, Cybister (Neocybister) festae Griffini, 1895, and Cybister (Neocybister) puncticollis (Brullé, 1837) re reviewed and diagnosed with the former redescribed and its type specimens considered for the first time since its description. Another evidently new species and possible new genus, Megadytes species, IR57 (
La clasificación de Cybistrinae Sharp, 1880 neotropicales (Coleoptera: Adephaga: Dytiscidae) se revisa ampliamente con base en un análisis filogenético de características morfológicas del grupo. Un nuevo género, Nilssondytes gen. nov. se describe para la única nueva especie Nilssondytes diversus sp. nov. de Venezuela. Se encontró que el género, Megadytes Sharp, 1882, del Nuevo Mundo y con varios subgéneros, no es monofilético. Se encontró que la especie tipo de Megadytes, Dytiscus latus Fabricius, 1801 y la especie Cybister parvus Trémouilles, 1984 forman un grupo monofilético y filogenéticamente más estrechamente relacionado con Cybister Curtis, 1827 que con otras especies asignadas a Megadytes sensu stricto, que se encontró que también forman un grupo monofilético. El nombre Megadytes se restringe aquí para incluir solo a Megadytes latus y Megadytes parvus. Se revisan y diagnostican estas dos especies asignadas a este nuevo concepto restringido del género. Un nuevo nombre, Metaxydytes gen. nov., se erige para incluir a todas las demás especies actualmente asignadas a Megadytes sensu stricto. Los nombres subgenéricos actuales asignados a Megadytes, Bifurcitus Brinck, 1945, Paramegadytes Trémouilles y Bachmann, 1980 y Trifurcitus Brinck, 1945, se elevan al rango de género, nuevo estado, ya que son parafiléticos de diversas formas. Se revisan y diagnostican las dos especies asignadas a Cybister (Neocybister) Miller, Bergsten y Whiting, 2007, Cybister (Neocybister) festae Griffini, 1895 y Cybister (Neocybister) puncticollis, redescribiendo la primera y considerando sus especímenes tipo por primera vez desde su descripción. Otra especie evidentemente nueva y posible nuevo género, Megadytes, IR57 (
Diving beetle, phylogeny, South America, taxonomy, water beetle
Cybistrinae Sharp, 1880 prior to this paper included seven genera, some with subgenera, from throughout much of the world, but especially in lower latitudes. The classification of the group was phylogenetically revised most recently by
Cybistrines in the Neotropical region occur especially in sunny lentic situations with extensive emergent vegetation, although they may be found in many aquatic habitats. Some species can be abundant at certain sites, but many are only rarely collected and are uncommon in collections. Neotropical cybistrines include the largest diving beetles in the world (
Upon the discovery of new taxa and reevaluation of certain described species with some unique character combinations, it became clear that the situation with Cybistrinae in South America is more complicated than the current classification reflects. The goal of this paper is to revise the Neotropical Cybistrinae genus groups and some of the species groups. The largest group of Neotropical species, historically placed in Megadytes, is not reviewed here and remains in need of revision with only analysis of the southern species having been made by
Methods for specimen preparation and examination largely follow
Specimens were examined or are referenced from the following collections:
Measurements are based on the range of available specimens and/or published values. Measurements were taken either using a standard steel ruler (longer measurements) or an ocular scale on a Zeiss Discovery V8 dissecting microscope at 50× magnification (shorter measurements). Emphasis was placed on measuring the largest and smallest specimens to describe the range of size in a species. Measurements include: (1) total length (TL); (2) greatest width across elytra (GW); (3) greatest pronotal width (PW); (4) greatest width of the head (HW); (5) distance between the eyes (EW); (6) narrowest width of metaventral wing (MV, Fig.
Male and female genitalia were dissected using methods similar to
Distribution data are based on examined specimens and published accounts for better-known species. Species historically placed in Megadytes have not been revised, and there may be confusion regarding their species identities in publications, so only type localities are referenced for these unrevised groups.
Fresh material suitable for DNA sequence acquisition and analysis was unavailable for many of the new and reinterpreted taxa treated here. Therefore, phylogenetic analysis is based on morphological characters historically used for these groups and a subset of taxa representative of the evident phylogenetic diversity and morphological combinations exhibited by Cybistrinae taxa (e.g.,
Numerous characters relevant to Cybistrinae phylogeny are reviewed by
One of these problematic characters is the nature of the metatarsal claws (Character (hereafter Char. 25). In certain Australian and Afrotropical Cybistrinae genera (Austrodytes Watts, Onychohydrus Schaum & White, Regimbartina Chatanay, Spencerhydrus Sharp & Sternhydrus Brinck), the metatarsal claws are unequal in length with the anterior claw shorter than the posterior. But in those species historically placed in Megadytes and Cybister the claws are characterized by a wider variety of configurations (Figs
Numbers and relative lengths of metatarsal claws in males and females of genera of Cybistrinae.
Male | Female | |
---|---|---|
Austrodytes | 2 claws, anterior < posterior | 2 claws, anterior < posterior |
Spencerhydrus | 2 claws, anterior < posterior | 2 claws, anterior < posterior |
Sternhydrus | 2 claws, anterior < posterior | 2 claws, anterior < posterior |
Onychohydrus | 2 claws, anterior < posterior | 2 claws, anterior < posterior |
Regimbartina | 2 claws, anterior < posterior | 2 claws, anterior < posterior |
Nilssondytes | 2 claws, anterior > posterior | 2 claws, anterior > posterior |
Bifurcitus | 2 claws, anterior = posterior | 2 claws, anterior = posterior |
Trifurcitus | 2 claws, anterior = posterior | 2 claws, anterior = posterior |
Metaxydytes | 2 claws, anterior = posterior | 2 claws, anterior > posterior |
Paramegadytes | 2 claws, anterior = posterior | 2 claws, anterior > posterior |
Megadytes | 2 claws, anterior > posterior | 2 claws, anterior > posterior |
Cybister | 1 claw | Some species with 1 claw, some species with 2 claws, anterior > posterior, few species dimorphic, either 1 claw or 2 claws, if 2, anterior > posterior |
Another complicated set of characters includes the male genitalia. The medial margin of male abdominal sternite IX (Char. 31) is either linear (with each medial margin together parallel, Figs
The female reproductive tract (RT) in Cybistrinae is distinctive and requires explanation. In cybistrines there is a single genital opening with an extremely long, heavily muscular vagina (
A particularly problematic set of characters is the subdivisions of antennomeres and maxillary and labial palpomeres in larvae (Chars 45–53). Species of Dytiscinae and Cybistrinae in particular, but other groups as well, have subdivided antennomeres and maxillary and labial palpomeres in various instars giving these structures the appearance of a greater number of segments. Technically they are not additional segments, but are instead subdivisions called articles by
The matrix was developed and trees were examined and analyzed using WinClada (
Cybistrini Sharp, 1880, as group of ‘Dytisci complicati’.
Cybister Curtis, 1827.
These are large to very large Dytiscidae (length 13.0–47.0 mm). The subfamily is demonstrably monophyletic and is characterized by the following synapomorphies (among others): in adults (
Cybistrinae prior to this study included seven genera, several with single or few species and Megadytes and Cybister, each of which are species rich and include multiple subgenera. The most recent phylogenetic classification of the group was developed by
The subfamily Cybistrinae has long been associated with Dytiscinae as a tribe of that subfamily and sister to the rest of the clade (e.g.,
Cybistrinae larvae are very characteristic within Dytiscidae (see diagnostic features above). They are often prominent and abundant large predators in systems where they occur. Knowledge of larvae in the group is increasing, but lags behind knowledge of adults, and even lags well behind knowledge of larvae of other diving beetle groups, despite their conspicuousness, although they have been investigated within the context of the phylogeny and taxonomy of Dytiscinae and Cybistrinae (
Descriptive knowledge of each larval instar for Cybistrinae. Known instars indicated with “X”.
Instar | Citations | |||
---|---|---|---|---|
I | II | III | ||
Austrodytes | None | |||
Bifurcitus | X |
|
||
Cybister (Cybister) | X | X | X |
|
Cybister (Megadytoides) | None | |||
Cybister (Melanectes) | None | |||
Cybister (Neocybister) | None | |||
Megadytes | X |
|
||
Metaxydytes | X | X | X |
|
Nilssondytes | None | |||
Onychohydrus | X | X | X |
|
Paramegadytes | X | X | X |
|
Regimbartina | None | |||
Spencerhydrus | X | X | X |
|
Sternhydrus | X | X | X |
|
Trifurcitus | X |
|
Cybistrinae are found throughout the world, mainly at low latitudes. Most members of the group are tropical, although some occur north to southern Canada and northern Europe and south through temperate South America and Australia and throughout southern Africa.
Parsimony analysis of the matrix resulted in seven equally parsimonious cladograms (length 102, CI = 68, RI = 93) one of which is shown in Fig.
Cybistrinae and Dytiscinae have historically been regarded as individually monophyletic and together monophyletic (with cybistrines as a tribe within Dytiscinae) based on a large number of adult and larval morphological characters (e.g.,
An analysis of Cybistrinae and reclassification was presented by
The analysis presented here is somewhat limited as regards taxon sampling overall, but it expands the Cybistrinae taxa available with morphological data and results largely support previous analyses including; 1) monophyly of Cybistrinae, 2) monophyly of the Australian genera (Regimbartina not included here) 2) monophyly of Cybister (except Cybister parvus), and 3) monophyly of taxa previously included in Megadytes together with Cybister (Figs
Bifurcitus Brinck, 1945: 8.
Cybister giganteus Laporte, 1835: 99 by original designation (= Dytiscus lherminieri Guérin-Méneville, 1829).
Within Cybistrinae Bifurcitus have (1) the lateral margins of the pronotum and elytra margined with yellow, (2) males and females each with two equal-length metatarsal claws, and (3) the posterior metatibial spur bifid (Figs
Bifurcitus is sister group to the similar Trifurcitus (Figs
Although previous evidence suggested that the several subgenera of “Megadytes” are monophyletic, monophyly of this group is not supported here based in part on the discovery of undescribed cybistrine species with unique combinations of character states (Figs
There are three currently valid species in Bifurcitus which were differentiated and characterized recently by
Dytiscus lateralis Fabricius, 1798.
Within Cybistrinae Cybister is characterized by the following: (1) a series of setae present along the posteroventral apical margin of the mesotarsomeres of males and pro- and mesotarsomeres of females (Fig.
Cybister are found in all major biogeographic regions but are most diverse in the Afrotropical and Oriental regions, mainly in low latitudes. The group is not diverse in the Neotropical region where it is largely replaced in numbers of species and individuals by species previously in Megadytes (Megadytes) (most of these in a newly described genus, see below).
Cybister is the sister group to Megadytes as newly constituted (Figs
South of Mexico and Caribbean islands including Cuba and the Bahamas.
1 | Size larger (TL = 26.6–27.6 mm); male median lobe in ventral aspect apically broadly expanded, apex very broad, subtruncate with medial, small point or projection, median lobe broadly expanded medially and apically making lateral margins distinctly sinuate (Fig. |
Cybister puncticollis (Brullé) |
– | Size smaller (TL = 20.3–21.7 mm); male median lobe in ventral aspect apically very slightly expanded, apex truncate without medial small point or projection, median lobe slightly expanded laterally in basal half, but margins not characteristically sinuate (Fig. |
Cybister festae (Griffini) |
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.
Cybister festae Griffini, 1895: 1.
Cybister (Meganectes) festae:
Cybister (Neocybister) festae:
Panama, Darién, Matusagrati Lake (Laguna della Pita).
The syntype specimens are in Museo Regionale di Scienze Naturali di Torino (Museum of Turin,
This species differs from the other Neotropical Cybister species, C. puncticollis, in smaller size (TL = 20.3–21.7 mm in C. festae vs. 26.6–27.6 mm in C. puncticollis) and the shape of the male genitalia. The male median lobe in C. puncticollis is apically broadly expanded (Fig.
Measurements. TL = 20.3–21.7 mm, GW = 11.7–13. mm, PW = 8.8–9.2 mm, HW = 5.1–5.5 mm, EW = 2.9–3.0 mm, TL/GW = 1.7–1.8, HW/EW = 1.7–1.8, WC/WV = 4.3–4.4. Body shape 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-black, clypeus and labrum pale yellow. Pronotum dark green-black, with broad lateral yellow marginal band, medial margin of band distinctly delimited, band separated from posterolateral margin by narrow green strip (Fig.
Sculpture and structure. Head broad, anteriorly produced, eyes prominent; dorsal surface evenly covered with exceptionally fine micropunctures but appearing smooth and shiny. Pronotum with lateral margins evenly and shallowly curved; surface of pronotum similar to surface of head in micropunctation; pronotum dorsally evenly curved. Elytron with margins very broadly curved, more strongly curved posteriorly; surface similar to surface of head in micropunctation and surface appearance. Prosternal process anteriorly rounded, surface nearly flat throughout and moderately broad, apex broadly elongate and sharply pointed. Metaventral wing narrow (WC/WV = 4.3–4.4); surface smooth, with extremely fine microsculpture, shiny. Lateral portion of metacoxa large, broad, surface smooth and shiny, with extremely fine microsculpture; metacoxal lines short and strongly curved, well-incised, extending anteriorly less than half distance across metacoxa. Abdominal ventrites smooth, unsculptured.
Male genitalia. Male median lobe in lateral aspect slender throughout length, apically slender, straight, and apically pointed, dorsal sclerite slender, evenly curved basally, apically straight, and slender, (Fig.
Female genitalia (Fig.
Sexual dimorphism. Males have a broad protarsal palette with ventral adhesive setae with apical structures in the form of elongate flattened spatulate surfaces; males also have mesotarsomeres with posteroventral fields of setae which are absent in females. Females lack natatory setae along the ventral margins of the metatarsomeres, but these are present in males. Males have a single metatarsal claw (the anterior, Fig.
Variation. Two specimens were examined, a male and a female. The female has the extent and intensity of greenish-rufous coloration somewhat greater than the male and is larger, but otherwise the two specimens are similar.
This species is known from the type locality in the Darién in Panama (
The lectotype (here designated) in
Dyticus puncticollis Brullé, 1837: 46.
Cybister puncticollis: Aubé 1838: 52.
Trogus puncticollis: Gemminger and Harold 1868: 460.
Megadytes puncticollis:
Cybister (Meganectes) kemneri
Brinck, 1945: 18;
Cybister (Meganectes) puncticollis:
Cybister (Neocybister) puncticollis:
Cybister puncticollis: Bolivia, San Miguel. Cybister kemneri: Brazil, La Plata, Amazonas, Rio Autaz.
Cybister puncticollis, in
This species is larger (Fig.
Measurements. TL = 26.6–27.6 mm, GW = 15.0–15.9 mm, PW = 10.8–11.6 mm, HW = 6.5–6.8 mm, EW = 3.7–3.8 mm, TL/GW = 1.7–1.8, HW/EW = 1.7–1.8, WC/WV = 2.9–3.2. Body shape oval, widest slightly posterad of middle; lateral margins broadly curved, continuously curved between pronotum and elytron. Depressed and somewhat flattened in lateral aspect.
Coloration. Head dark green, clypeus and labrum pale yellow. Pronotum dark green, with broad lateral yellow marginal band (Fig.
Sculpture and structure. Head broad, anteriorly produced, eyes prominent; dorsal surface evenly covered with exceptionally fine micropunctures but smooth and shiny. Pronotum with lateral margins evenly and shallowly curved; surface of pronotum similar to surface of head in micropunctation; pronotum dorsally evenly curved. Elytron with margins very broadly curved, more strongly curved posteriorly; surface similar to surface of head in micropunctation and surface appearance. Prosternal process anteriorly distinctly emarginate medially, remaining surface nearly flat throughout and moderately broad, apex broadly elongate and sharply pointed. Metaventral wing narrow (WC/WV = 2.9–3.2); surface smooth, with extremely fine microsculpture, shiny. Lateral portion of metacoxa large, broad, surface smooth and shiny, with extremely fine microsculpture; metacoxal lines short and curved, extending anteriorly less than half distance across metacoxa. Abdominal ventrites smooth, relatively unsculptured.
Male genitalia. Male median lobe in lateral aspect moderately slender throughout, evenly curved, apically abruptly expanded with a narrowly rounded apex, ventral sclerite slender and evenly curved basally, apically straight and apically pointed (Fig.
Female genitalia. Vagina extremely elongate, slender; with enlarged area at base of common oviduct and spermatheca, with enlarged lateral sacs on this enlarged area; spermatheca extremely slender and elongate (Fig.
Sexual dimorphism. Males have a broad protarsal palette with ventral adhesive setae with apical structures in the form of elongate flattened spatulate surfaces; males also have mesotarsomeres with posteroventral fields of setae which are absent in females. Females lack natatory setae along the ventral margins of the metatarsomeres, but these are present in males. Males have a single metatarsal claw (the anterior claw, Fig.
Variation. Specimens vary somewhat in size and coloration, with some specimens more greenish and others darker, less greenish.
This species is known from Argentina, Bolivia, Brazil, French Guyana, and Peru. There is also a previously unpublished record from Paraguay.
Specimens were examined from Argentina, Bolivia, Peru, and Paraguay.
Megadytes Sharp, 1882: 701.
Megadytes latus Fabricius, 1801: 260.
The concept of the genus presented here differs significantly from previous ones (e.g.,
Within Cybistrinae Megadytes are similar to Cybister (Figs
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.
Megadytes is sister to Cybister (Figs
1 | Size larger (TL = 19.5–23.2 mm), and relatively broader (TL/GW = 1.7–1.8) (Fig. |
Megadytes latus (Fabricius) |
– | Size smaller (TL = 13.0–14.6 mm), and relatively narrower (TL/GW = 1.9–2.1) (Fig. |
Megadytes parvus (Trémouilles) |
Dytiscus latus Fabricius, 1801: 260.
Trogus latus: Gemminger and Harold 1868:459.
Megadytes latus:
Cybister (Megadytes) latus: Wilke 1921: 248.
Megadytes lata:
Megadytes (Megadytes) latus:
South America.
Syntypes in Zoological Museum der Universität Kiel, Germany, not examined.
This species differs from M. parvus in its larger size (TL = 19.5–23.2 mm in M. latus, Fig.
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.
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.
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
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 (
This species is known from Argentina, Brazil, French Guiana, Uruguay (
Few specimens of this species exist in collections. Two specimens from Argentina, one from Bolivia (new country record), one from Brazil (
Cybister parvus Trémouilles, 1984: 187.
Brazil, Bahia State, Santa Rita.
Holotype and nine paratypes in Museu de Zoologia, Universidade de São Paulo, Brazil and two paratypes, one male and one female, in Museo de La Plata, La Plata, Argentina.
This species differs from the other species in the genus, M. latus, in smaller size (TL = 13.0–14.6 mm), narrower shape (TL/GW = 1.9–2.1) (Fig.
Measurements. TL = 13.0–14.6 mm, GW = 6.2–7.7 mm, PW = 5.4–5.9 mm, HW = 3.3–3.4 mm, EW = 2.0–2.1 mm, TL/GW = 1.9–2.1, HW/EW = 1.6–1.7, WC/WV = 4.1–4.8. Body shape elongate oval, widest slightly posteriad of middle; lateral margins broadly curved, continuously curved between pronotum and elytron (Fig.
Coloration. Head dark green to green-rufous throughout. Pronotum dark green with broad lateral green-rufous margins. Elytron dark green with broad lateral green-rufous margins. Ventral surfaces dark rufous.
Sculpture and structure. Head broad, anteriorly produced, eyes prominent; dorsal surface evenly covered with extremely fine microsculpture and micropunctures. Pronotum with lateral margins evenly and broadly curved; surface similar to surface of head in microsculpture and micropunctation; pronotum somewhat swollen anteriorly. Elytron with margins very broadly curved; surface similar to surface of head in microsculpture, but with extensive, very fine micropunctation. Prosternal process anteriorly rounded, surface flat and broad, apex 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, extending anteriorly less than half distance across metacoxa. Abdominal ventrites smooth, unsculptured.
Male genitalia. Male median lobe in lateral aspect broad throughout, subapically somewhat expanded, apically narrowed, apex with multiple small processes (Fig.
Female genitalia. The single female specimen available for examination lacks female genitalia which apparently have been dissected and lost.
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 unequal length metatarsal claws with the posterior shorter, but in males the posterior claw is relatively longer than in females, and distinctly, but only somewhat, shorter than the anterior (~ 4/5 of length).
Variation. Two paratype specimens were examined, a male and a female. The female has the extent and intensity of greenish-rufous coloration somewhat greater than the male, but otherwise the two specimens are similar.
This species is known only from Santa Rita, Bahia State, Brazil. Indication by
Nothing is known of the habitat of this species.
Twelve specimens in
Megadytes sensu auctorum.
Megadytes fraternus Sharp, 1882: 708, by current designation.
These species have males with equal-length metatarsal claws and females with two claws of unequal length with the posterior claw distinctly reduced (Figs
Metaxydytes is from the Greek metaxy, meaning “between,” and dytes, meaning “diver,” the root word for many genera of Dytiscidae including in this subfamily. The genus is named to signify its intermediate phylogenetic placement among other genera of Cybistrinae.
This genus may be sister group to Paramegadytes based especially on the presence of distinctive stiff, spinous setae along the medial margins of the female gonocoxosternite (
These species were previous placed in Megadytes. The type species of Megadytes s. str. is M. latus which belongs to a different genus from all other known species previously placed in Megadytes (Figs
Nilssondytes diversus sp. nov., by current designation.
From other Cybistrinae this genus differs in having: (1) the metatibial spurs apically simple, (2) metacoxal lines clearly present, (3) the pronotum and elytron with broad, distinct lateral yellow bands along margins (Fig.
This genus is named Nilssondytes from the Latin dytes meaning “diver,” and Nilsson, after the great diving beetle worker and excellent friend, Anders Nilsson, in honor of his inestimable contribution to the science of diving beetle biology.
The single species of Nilssondytes is part of the clade that includes species with an oblique metatrochanteric groove, but it has an unresolved position with respect to other genera (Figs
Venezuela, Amazonas State, roadside pond ca. 7 km S Samariapo 5°10.900'N, 67°46.078'W, 95 m elev.
This is the only species in the genus and is characterized by its diagnostic combination (see above). Typically, species-level features include the shape of the male median lobe which is unique. In ventral aspect the apex is abruptly constricted with the apex narrowly truncate with laterally pointed processes (Fig.
Measurements. TL = 16.7–19.4 mm, GW = 9.6–10.7 mm, PW = 7.0–8.1 mm, HW = 4.2–4.7 mm, EW = 2.7–2.9 mm, TL/GW = 1.7–1.8, HW/EW = 1.6–1.7, WC/WV = 3.1–3.2. Body shape suboval, slightly expanded posteriorly, widest at ~ 3/5 of length; lateral margins evenly, continuously curved between pronotum and elytron. Depressed and somewhat flattened in lateral aspect (Figs
Coloration
(Figs
Sculpture and structure. Head broad, frontoclypeal lines elongate, straight, strongly oblique; anterior clypeal margin broadly, shallowly, and evenly concave; dorsal surface evenly covered with fine microsculpture and micropunctures. Pronotum with lateral margins evenly and broadly curved; surface similar to surface of head in microsculpture and micropunctation. Elytral lateral margin evenly and slightly curved for most of length, apically broadly curved; surface of elytron similar to surface of head in microsculpture and micropunctation. Prosternal process apically rounded, ventral surface distinctly sulcate, apex robust, acutely pointed. Metaventral wing broad, slightly less than 1/3 width of lateral portion of metacoxa (WC/WV = 3.1–3.2); surface smooth, without sculpturing. Lateral portion of metacoxa large, broad, surface smooth, without sculpturing; metacoxal lines short, extending less than half distance across metacoxa. Abdominal ventrites smooth, unsculptured.
Male genitalia. Male median lobe in lateral aspect shallowly curved, apically abruptly narrowed, apex narrowed, slightly curved, apically narrowly rounded, broad medially (Fig.
Female genitalia. With a single genital opening, vagina elongate, slender, with enlarged, bulbous region at base of common oviduct; spermatheca short, curved, at apex of enlarged region, with soft tissue region on each side of enlarged region (Fig.
Sexual dimorphism. Males have a characteristic broad protarsal palette with ventral adhesive setae. Males also have mesotarsomeres with clumps of posteroventral setae. Females lack pro- and mesotarsal expansions or adhesive setae. Both males and females have two metatarsal claws with the posterior shorter than the anterior, but females have the posterior somewhat more curved than in males (Figs
Variation. Five specimens were examined. One specimen has the lateral pronotal yellow band extending to the posterior margin of the pronotum, the others have a narrow dark green separation from the posterior margin.
This species is known from few localities in Venezuela along the northwestern margins of the Guiana Shield craton (Fig.
The only natural history information available from labels is “roadside pond,” “river margin,” and “rock outcropping.”
The species is named from the Latin diversus, meaning “different,” in recognition of the different lengths of the metatarsal claws in both males and females (Figs
Holotype , male labeled, “VENEZUELA: Amazonas State 5°10.900'N, 67°46.078'W, 95 m ca. 7 km S. Samariapo 15.i.2009; leg. Short, Miller, García, Camacho, Joly VZ09-0115-02X: roadside pond/ SM0846115 KUNHM-ENT [barcode label]/ HOLOTYPE: Nilssondytes diversus Miller, Michat and Ferreira-Jr., 2023 [red label with double black line border].” Paratypes, 1 male labeled, “Suapure VENEZ. Caura River 4.20.1900 [handwritten] E.A. Klages.”, 1 female labeled “VENEZUELA: Bolivar State 7°41'23.6"N, 64°1'56.0"W, 134 m ca. 14 km E Rio Aro; 5.viii.2008 leg. A. Short $ M. García AS-08-073; rock outcropping/ SM0829328 KUNMH-ENT [barcode label],” 1 female labeled “VENEZUELA: Guárico State 8°6.226'N, 66°26.228'W, 52 m UCV San Nicolasito Field Station: Rio Aguaro; 10.i.2009 leg. Short, Miller, Joly, García, Camacho; VZ09-0110-01A/ SEMC0852602 KUNHM-ENT,” 1 male labeled “VENEZUELA: Bolivar State 6.58694°N; 67.02912°W Rio Caripito 12.i.2009; leg. Short Miller VZ09-0112-02A: river margin/ SM0844405 KUNHM-ENT [barcode label].” All paratypes with, “…PARATYPE Nilssondytes diversus Miller, Michat and Ferreira-Jr., 2023 [blue label with black line border].”
Paramegadytes Trémouilles & Bachmann, 1980: 101.
Dyticus glaucus Brullé, 1837: 46 by original designation.
Like Metaxydytes these species have both metatibial spurs apically simple, the medial margins of male abdominal sternite IX straight, and both males and females with two metatarsal claws, males with equal-length claws and females with the posterior claw reduced (Figs
This may be the sister genus to Metaxydytes (Figs
There are currently two valid species in this genus, P. australis (Germain) and P. glaucus (Brullé).
Trifurcitus Brinck, 1945: 8.
Cybister fallax Aubé, 1838b: 54, by original designation.
These are former Megadytes species with the anterior metatibial spur apically trifid (Fig.
Trifurcitus is sister group to Bifurcitus (Figs
See above under Bifurcitus for more discussion of these two taxa. Six species are currently recognized. Although they have not been revised thoroughly, most of the species were described or illustrated by
Megadytes
species IR57:
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
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 “IR57” (
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 “IR57” (
Peru, Atalapa, Rio Carbon at Rio Madre de Dios, in river, Apr 1999 (
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.
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.
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.
A single male specimen examined labeled, “271297 PERU ZUNGARO COHA 16u:TO [handwritten, somewhat illegible].”
Adapted from
1 | Posterior metatibial spur bi- or trifurcate (e.g., Figs |
2 |
– | Posterior metatibial spur simple (e.g., Fig. |
3 |
2 | Posterior metatibial spur bifurcate (Figs |
Bifurcitus Brinck, stat. nov. |
– | Posterior metatibial spur trifurcate | Trifurcitus Brinck, stat. nov. |
3 | Prosternal process longitudinally conspicuously sulcate; Australian and Neotropical | 4 |
– | Prosternal process without longitudinal sulcus although lateral margins may be variously bordered and anterior portion may be shallowly sulcate or excavated; distribution various | 6 |
4 | Metacoxal lines absent | Sternhydrus Brinck |
– | Metaxocal lines present | 5 |
5 | Prosternal process longitudinally narrowly and deeply sulcate throughout length; male and female each with metatarsal claws unequal in length, anterior claw shorter than posterior claw | Spencerhydrus Sharp |
– | Prosternal process longitudinally broadly sulcate, mainly in anterior half; male and female each with metatarsal claws unequal in length, posterior claw rudimentary and short (Figs |
Nilssondytes gen. nov. |
6 | Metacoxal lines absent; Australian | Onychohydrus Schaum |
– | Metacoxal lines present; distribution various | 7 |
7 | Male with a single metatarsal claw, female either with one claw or with an additional, small posterior rudimentary claw (Figs |
8 |
– | Male and female with two metatarsal claws, in some cases with posterior claw rudimentary and small (Figs |
11 |
8 | Elytron without distinct yellow lateral margins; female always with a second, rudimentary posterior metatarsal claw | 9 |
– | Elytron with distinct yellow lateral margins; female with either a single metatarsal claw or with a second rudimentary posterior claw | 10 |
9 | Pronotum with distinct yellow lateral margins | Cybister (Megadytoides) Brinck |
– | Pronotum without distinct yellow lateral margins | Cybister (Melanectes) Brinck |
10 | Female with a single metatarsal claw or, in few species, dimorphic with some specimens with a second, rudimentary posterior claw; apex of dorsal sclerite of male median lobe various, but not bifid; medial margin of female gonocoxosternite straight or slightly concave; distribution North and Central America, Africa, Eurasia and Australia, absent from most of Neotropical Region except Mexico and certain Caribbean islands | Cybister (Cybister) Curtis |
– | Female always with two metatarsal claws, posterior claw short and curved (Figs |
Cybister (Neocybister) Miller, Bergsten & Whiting |
11 | Dorsal surface light green with sparsely distributed, small black dots, laterally without distinct pale margins; central Afrotropical | Regimbartina Chatanay |
– | Dorsal surface dark green to green-black without black dots, laterally with or without distinct pale margins; Australian, Nearctic or Neotropical | 12 |
12 | Prosternal process with distinct lateral carinae; male and female metatarsal claws similar, anterior claw shorter than posterior; dorsal surface dark green with distinct lateral pale margins; Australian | Austrodytes Watts |
– | Prosternal process without distinct lateral carinae; male and female claws various, male with either equal-length metatarsal claws or with posterior claw reduced, shorter than anterior, female with two claws, posterior reduced, shorter than anterior (Figs |
13 |
13 | Male and female both with two metatarsal claws, anterior claw shorter than posterior (Figs |
Megadytes Sharp |
– | Male with two metatarsal claws that are subequal in length, female with two metatarsal claws, with posterior claw shorter, rudimentary (Figs |
14 |
14 | Size large, TL ≥ 27 mm; metasternal wings relatively broad (WC/WV = 1.8–1.9) | Paramegadytes Trémouilles & Bachmann, stat. nov. |
– | Size smaller, TL ≤ 24 mm; metasternal wings relatively narrow (WC/WV = 2.5–2.6) | Metaxydytes , gen. nov. |
Nilssondytes and Cybister (Neocybister) not included (larvae unknown)
1 | Median lobe of frontoclypeus apically sharp, without apical tuft of setae (Fig. |
Trifurcitus Brinck, stat. nov. |
– | Median lobe of frontoclypeus apically truncate, with apical tuft of setae (Figs |
2 |
2 | Median and lateral lobes of frontoclypeus separated by a narrow emargination (Fig. |
Metaxydytes , gen. nov. |
– | Median and lateral lobes of frontoclypeus separated by a wide emargination (Figs |
3 |
3 | Lateral lobes of frontoclypeus bilobed (Fig. |
Paramegadytes Trémouilles & Bachmann, stat. nov. |
– | Lateral lobes of frontoclypeus with a single lobe (Figs |
4 |
4 | Lateral lobes of frontoclypeus acute (Fig. |
Megadytes Sharp |
– | Lateral lobes of frontoclypeus obtuse (Fig. |
Bifurcitus Brinck, stat. nov. |
Bifurcitus Brinck, 1945, stat. nov.
Bifurcitus magnus (Trémouilles & Bachmann, 1980: 118); Argentina, Santa Fe.
Cybister Curtis, 1927
Cybister (Neocybister) Miller, Bergsten, & Whiting, 2007
Megadytes Sharp, 1882
Metaxydytes , new genus
Nilssondytes , gen. nov.
Paramegadytes Trémouilles & Bachmann, 1980, stat. nov.
Trifurcitus Brinck, 1945, stat. nov.
Neotropical Cybistrinae incertae sedis with respect to genus
One of seven cladograms derived from parsimony analysis of 57 morphological characters from Cybistrinae and other Dytiscidae (len = 105, CI = 68, RI = 92) with characters mapped using ‘fast’ optimization in WinClada. Black hash marks indicate unambiguous changes, white hash marks indicate homoplasious changes or reversals. Numbers above hash marks are character numbers, those below hash marks are derived state numbers.
KBM thanks A.E.Z. Short for collaboration in Venezuela.
The authors have declared that no competing interests exist.
No ethical statement was reported.
Portions of this project were funded by NSF grants #DEB–1353426, #DEB–0845984, and #DEB–0816904 (KBM and A.E.Z. Short, PIs).
All authors have contributed equally.
Kelly B. Miller https://orcid.org/0009-0004-1093-4066
Mariano C. Michat https://orcid.org/0000-0002-1962-7976
Nelson Ferreira Jr https://orcid.org/0000-0002-5932-7695
All of the data that support the findings of this study are available in the main text or Supplementary Information.
Morphological characters used in phylogenetic analysis. Citations are provided for previous use of the characters in phylogenetic analyses. These should be consulted for more detailed descriptions and review of these characters.
Adult
Head
Thorax
Legs
Abdomen
Male genitalia
Female genitalia
Larva
Head
Abdomen
Character coding for phylogenetic analysis
Data type: docx