Chasmogenus fluminensis, Clarkson, Bruno & Ferreira-Jr, Nelson, 2014

Clarkson, Bruno & Ferreira-Jr, Nelson, 2014, Four new species and first nominal record of Chasmogenus Sharp, 1882 (Coleoptera: Hydrophilidae) from Brazil, Zootaxa 3765 (5), pp. 481-494 : 484-487

Chasmogenus fluminensis sp. nov.

(Figs. 1, 2, 9, 10, 11, 12, 23, 27 and 28)

Type material. Holotype (male): “ BRASIL: Rio de Janeiro,/ Rio de Janeiro,/ Parque Nacional da Tijuca/ 10.I.1991, 22°58’13” S 43°15’25” O,/ Ferreira-Jr, N. col.” ( DZRJ, Coleoptera 3175). Paratypes (38): BRAZIL. RIO DE JANEIRO STATE. Nova Friburgo Municipality: (2 ex.: DZRJ, Coleoptera 2781 ; 2 ex.: SEMC); “Alto Cascatinha, folhiço de correnteza, 28.IV.1995, Dorvillé, L. F. col.” (1 ex.: DZRJ, Coleoptera 2788 ); Rio de Janeiro Municipality: Same data as Holotype (5 ex.: DZRJ, Coleoptera 1763 ); Teresópolis Municipality: “Serra do Subaio, rio da Varginha, Represa do Hotel Sayonara, 06.X.2004 ” (2 ex.: DZRJ, Coleoptera 2843 ); “Faz. Vale da Revolta, Poça na Mata, 12.X.1996, 22º26’56” S 42º56’31” W, Ferreira-Jr, N. col.” (1 ex.: DZRJ, Coleoptera 1483 ); Same locality, “rio Paquequer, folhiço flutuante, 19.VIII.1996, 22º26’56” S 42º56’31” W, Ferreira-Jr, N. col.” (1 ex.: DZRJ, Coleoptera 1750 ); Same locality, leg. and river, different dates: 15.II.1991, 13.IV.1991, 20.VII.1991, VII.1991, 20.VIII.1991, 19.X.1991, 13.II.1992, 28.I.1995, 12.X.1996 (18 ex.: DZRJ, Coleoptera 1751 , 1753, 1754, 1755, 1756, 1757, 1758, 1759, 1760, 1761, 1762, 1826, 1966, 2734, 2770, 2777; 2 ex.: MLPA; 2 ex.: MNRJ; 2 ex.: NHMW; 2 ex.: NMPC).

Diagnosis. Medium to large-sized species (3.45–4.85 mm). Head densely punctated. Anterior clypeal margin with narrow emargination, round to angulate shaped, exposing a gap between clypeus and labrum (Fig. 28). Anterior margin of labrum slightly concave medially. Anterocentral notch of mentum on raised anterior margin, developed and triangular (Figs. 10 and 11). General dorsal punctures of pronotum and elytra fine, much smaller than systematic punctures. Elytra with four weakly distinct longitudinal rows of systematic punctures in dorsal view (Fig. 1). Prosternum not carinate (Fig. 27). Mesoventral carina restricted to posterior half, slightly raised (Fig. 2). Hind femora pubescent on basal four-fifths (Fig. 2). Ventrite 5 with shallow apical emargination (Fig. 2). Phallobase short, manubrium distinct, narrow. Parameres notably shorter than median lobe, inner margin slightly emarginated on apical fifth, outer margin subparallel basally. Median lobe thick, gradually narrowing apicad, apex strongly acuminate; basal apophyses subparallel, within parameres (Fig. 23).

Given the body length range among the described species in the genus, as well as C. ubatuba sp. nov., C. fluminensis sp. nov. may be considered a medium to large species. Since only C. itatiaia sp. nov. presents larger specimens, the total length may help to diagnose the species. C. fluminensis sp. nov. presents the anterior clypeal margin rounded to angulate (Fig. 28), as well as C. bariorum , C. occidentalis and C. yukparum , in which it differs from the wide emargination with its mesal portion straight presented by C. australis and C. sapucay (Fig. 30). Anterocentral notch of mentum of C. fluminensis is triangular as in C. rufinasus , but is less conspicuous, in ventral view (Figs. 9, 10), than in the most part of species with rounded notch. Mentum is very strongly depressed on anterocentral half (Fig. 11). The absence of a strong carina raised into a “tooth” on the metaventrite distinguish this species from the Venezuelan species C. bariorum , C. occidentalis and C. yukparum . The overall shape of the male genitalia is diagnostic for this species (Fig. 23): characteristics as parameres conspicuously shorter than median lobe, evenly wide from base to apical third with outer margin subparallel basally, and median lobe with apex strongly acuminate distinguish this species from the other Neotropical species.

Description. Holotype male.

Size and form. Total length 4.20 mm; maximum width 2.05 mm; maximum width of head 1.05 mm; elytral length 2.60 mm; maximum width of pronotum 1.85 mm. Body broadly oval, moderately convex (Fig. 1).

Color. Dorsum of head, pronotum and elytra uniformly pale brown with front often darker (Fig. 1). Antennae, maxillary and labial palpi uniformly pale brown (Figs. 1 and 2). Ventral face and legs uniformly pale to medium brown (Fig. 2).

Head. Ground punctation on labrum, clypeus and frons fine, distance between punctures 1.5–2.0x the width of one puncture (Fig. 28). Systematic punctures on labrum consisting of several punctures about twice the diameter of surrounding punctures, forming an irregular row on median portion, sometimes bearing short, fine setae. Clypeus with an irregular row of distinct systematic punctures on anterior portion, in both sides, with few scattered ones, about twice larger than surrounding punctures, bearing short, fine setae (Fig. 28). Frons with irregular row of distinct systematic punctures along frontoclypeal suture, about 2.0–3.0× larger than surrounding punctures and some less distinct scattered systematic punctures mesally of eyes, both bearing short, fine setae. Anterior clypeal margin with narrow emargination, round to angulate shaped, exposing a gap between clypeus and labrum (Fig. 28). Anterior margin of labrum slightly concave medially. Mandibles bifid at apex. Maxillary palpi somewhat longer than maximum width of head (0.2x longer); palpomeres subequal in length (Figs. 1 and 2). Labial palpi about half the width of mentum; Ultimate palpomere with a preapical long seta (Fig. 12). Mentum bare, with some short setae on lateral margins, rather punctuate, somewhat rugose, with deep notch on anterolateral margin and very deeply depressed on anterocentral half; anterocentral notch on a raised anterior margin, developed and triangular (Figs. 9, 10 and 11).

PLATE 1. Figs. 1 and 2. Chasmogenus fluminensis sp. nov. habitus, 1: dorsal view, 2: ventral view; Figs. 3 and 4. Chasmogenus itatiaia sp. nov. habitus, 3: dorsal view, 4: ventral view; Figs. 5 and 6. Chasmogenus lilianae sp. nov. habitus, 5: dorsal view, 6: ventral view; Figs. 7 and 8. Chasmogenus ubatuba sp. nov. habitus, 7: dorsal view, 8: ventral view. Scale = 2.00 mm.

Thorax. Ground punctation on pronotum and elytra evenly distributed and very fine. Pronotum with two anterolateral and two posterolateral series of systematic punctures with short fine setae, each systematic punctures at least twice the size of surrounding ground punctures: anterior series forming an irregular row curved backwards, beginning near anterolateral corners toward medial portion of pronutum; posterior series forming an irregular row on posterior half, perpendicular to lateral margins, beginning near of margin, restricted to lateral quarter (Fig. 1).

Pronotal margins completely rimmed; lateral margins with some sparse systematic punctures without conspicuous setae; posterior margin slightly arcuate (Fig. 1). Elytra with four weakly distinct longitudinal irregularly spaced rows of systematic punctures in dorsal view, punctures about 4x larger than ground punctures, bearing long, fine setae; sutural stria strongly impressed on posterior three-fifths (Fig. 1). Prosternum finely pubescent, weakly convex, not carinate medialy (Fig. 27). Mesoventrite with a longitudinal carina on medial part, restricted to posterior half, well defined but only slightly raised (Fig. 2). Metaventrite with posteromedial, enlongate oval glabrous area, slightly longer than wide, about half the total length of metaventrite (Fig. 2). Hind femora pubescent on basal four-fifths (Fig. 2).

PLATE 2. Figs. 9–12 and 23. Chasmogenus fluminensis sp. nov., 9: anterior margin of mentum in ventral view, showing the anterocentral notch shape, 10: mentum in ventral view, 11: the same in posteroventral view, showing the deeply depression on anterocentral half and the raised anterior margin, 12: right labial palp in ventral view, showing the preapical seta on ultimate labial palpomere, 23: aedeagus in dorsal view; Figs. 13–15 and 26. Chasmogenus itatiaia sp. nov., 13: anterior margin of mentum in ventral view, showing the anterocentral notch shape, 14: mentum in ventral view, 15: the same in posteroventral view, showing the deeply depression on anterocentral half and the anterior margin shape, 26: aedeagus in dorsal view; Figs. 16, 17 and 24. Chasmogenus lilianae sp. nov., 16: anterior margin of mentum in ventral view, showing the anterocentral notch shape, 17: mentum in ventral view, 24: aedeagus in dorsal view; Figs. 18, 19 and 22. Chasmogenus sapucay Fernández , 18: anterior margin of mentum in ventral view, showing the anterocentral notch shape, 29: mentum in ventral view, 22: aedeagus in dorsal view; Figs. 20, 21, and 25. Chasmogenus ubatuba sp. nov., 20: anterior margin of mentum in ventral view, showing the anterocentral notch shape, 21: mentum in ventral view, 25: aedeagus in dorsal view. Scale = 0.25 mm.

Abdomen. Ventrites densely and evenly pubescent. Ventrite 5 with shallow posteromedial emargination, distinctly wider than deep, and lined with coarse yellow setae (Fig. 2). Aedeagus (Fig. 23) about 0.62 mm in length. Phallobase well developed, as long as wide, symmetrical, shorter than apical portion (ca. 0.35x the aedeagus in length), maximum width on apical third; manubrium distinct, narrow, rounded at base, about half the length of phallobase. Parameres conspicuously shorter than median lobe, evenly wide from base to apical third, were gradually narrowing apicad, inner margin slightly emarginated on apical fifth in dorsal view, outer margin subparallel basally; apex rounded, slightly turned inwards. Median lobe thick, gradually narrowing apicad, apex strongly acuminate; corona distinct, oval, wider than longer, subapical (on apical seven-tenths); basal apophyses subparallel, within parameres, almost extended into phallobase.

PLATE 3. Figs. 27 and 28. Chasmogenus fluminensis sp. nov., 27: prosternum, 28: head in dorsal view, showing the clipeolabral margin and systematic punctures; Fig. 29. Chasmogenus itatiaia sp. nov.: prosternum; Figs. 30 and 31. Chasmogenus australis García (modified from García 2000), 30: head in dorsal view, with the anterior clypeal margin; 31: aedeagus in dorsal view; Figs. 32 and 33. Chasmogenus occidentalis García (modified from García 2000), 32: mesoventral carina in lateral view, 33: aedeagus in dorsal view; Figs. 34 and 35. Chasmogenus bariorum García (Modified from Garcia 2000), 34: Mesoventral carina in lateral view, 35: aedeagus in dorsal view; Figs. 36 and 37. Chasmogenus yukparum García (modified from García 2000), 36: Mesoventral carina in lateral view; 37: Aedeagus in dorsal view.

Variation. Body length from 3.45 mm to 4.85 mm. Coloration: a few specimens exhibit darker dorsal coloration, but essentially pale brown. Sexual dimorphism in the external morphology was not observed in the type specimens.

Etymology. “ Fluminensis ” is the Latinized version of the Portuguese word “Fluminense”, in which is a popular name used to refer to those born in Rio de Janeiro State. This specific name refers to the wide distribution of the species in the state, as well as to its occurrence in backwater margins of streams, unusual among species of the genus.

Biology. The type and additional material were collected from lentic habitats like ponds and marshes, among the vegetation; from crenal and ritral sections of streams on backwater margins: among the vegetation, in sand bottom or in floating leaf litter; and from ǀeDf pDʗks in flowing water areas. The specimens were collected mainly in mountainous areas from 500 to 1400 m a.s.l., in Atlantic rain forest. For its wide range in inhabited habitats and environmental conditions, we may expect a wider distribution of this species.

Remarks. The new species shows a wide range of size (length from 3.45 to 4.85 mm), which is unusual for Neotropical Chasmogenus . The wide range of habitats, altitude and temperature observed on the distribution of the species may have influence on the total size of the species. It was observed that the specimens collected at high altitudes and lower temperatures are bigger. Some morphometric and ecological analyses are needed to confirm this hypothesis.