Chasmogenus Sharp, 1882

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 : 483

Chasmogenus Sharp, 1882

Chasmogenus Sharp, 1882: 73 .— Type species: Chasmogenus fragilis Sharp (monotypy).

Helochares (Chasmogenus) : Orchymont (1919: 149, downgraded to subgenus).

Chasmogenus: Fernández (1986: 189, elevated to genus) .

= Helochares (Crephelochares) Kuwert, 1890: 38 .— Type species: Helochares livornicus Kuwert, 1890 . Designated by Orchymont (1939: 154). Synonymized with Chasmogenus by Orchymont (1919: 148), synonymy confirmed by Fernández (1986: 189).

Diagnosis. Small to moderately sized (ca. 2.5–6.2 mm in length), round to elongate oval shaped in dorsal view, sometimes rather parallel-sided (e.g. Figs. 1–8); slightly convex in lateral view. Antennae with eight or nine antennomeres; maxillary palpi at least as long as width of head, often longer, 2nd palpomere slightly curved inwards (Figs. 1–8); mentum deeply notched anteromedially (e.g. Figs. 9–21). Elytra with systematic punctures arranged in rows which may be indistinct, often bearing short to long setae; with distinct sutural stria in posterior portion (e.g. Figs. 1, 3, 5 and 7). Prosternum well developed, weakly convex to tectiform, without or with medial carina (Figs. 27 and 29). Mesoventrite narrowed anteriorly and rather concave (Figs. 2, 4, 6 and 8), without or with a longitudinal medial carina (e.g. Figs. 32, 34 and 36). Metaventrite somewhat convex, with posteromedial portion hardly more raised (Figs. 2, 4, 6 and 8). Tarsal formula 5-5-5; hind tarsi with 2nd tarsomere much longer than 1st. Abdomen with five exposed ventrites, with fine and dense pubescence (Figs. 2, 4, 6 and 8); posterior margin of ventrite 5 with a shallow apical notch (modified from Hansen 1991).

Remarks. Characters of taxonomic importance for Neotropical species include: i) the aspect of the general dorsal punctures, which may be fine to moderately coarse and smaller to about same size of systematic punctures; ii) the apparent presence and overall condition of systematic punctures on head, pronotum and elytra; iii) the anterior clypeal margin, which may possess an emargination exposing a distinct gap between the clypeus and labrum or not, this emargination may be narrow or wide—Fernández (1986), Short (2005) and García (2000) described these emargination as triangular in some species or truncate centrally with anterolateral lobes (in C. sapucay Fernández ) or with anterolateral angles (in C. australis García )—based in Brazilian species, we observed that those species in which the emargination is narrow, the shape may vary among rounded and angulate, and those in which emargination is wide the mesal portion is straight; iv) the aspect and shape of anterocentral notch on mentum, which may be very deep and developed or reduced, and may be rounded or triangular; v) the ultimate labial palpomeres, which may present one or two conspicuous preapical long seta; vi) the prosternum, which may be more or less convex, and with or without a carina restricted to posterior portion; vii) the mesoventrite may have a longitudinal carina or not, which may be only slightly distinct to strongly raised in a large ‘tooth’ posteriorly; viii) the fifth abdominal ventrite, which may appear truncate apically or with a shallow apical emargination, which may be more or less developed.

The overall shape of male genitalia, mainly the aspect of the phallobase, parameres and median lobe, as well as the relative proportion between these structures, provides important characteristics for the Brazilian species diagnosis. Until now, all Brazilian species present a manubrium that is more or less distinct; parameres with apex rounded and inner margin somewhat sinuated or slightly emarginated on apical portion; and medial lobe more or less acuminate or blunt at apex.