Chiasognathus Stephens, 1831

Paulsen, M. J. & Smith, Andrew, 2010, Revision of the genus Chiasognathus Stephens of southern South America with the description of a new species (Coleoptera, Lucanidae, Lucaninae, Chiasognathini), ZooKeys 43 (43), pp. 33-63 : 38-41

Genus Chiasognathus Stephens, 1831

Chiasognathus Stephens, 1831: 213 . Type species: Chiasognathus grantii Stephens 1831 , by monotypy.

Tetropthalma Lesson, 1833 : plate 24. Type species T. chiloensis Lesson 1833 , by monotypy.

Bomansodus Chalumeau & Brochier, 1995: 20 . Type species Chiasognathus impubis Parry 1870 , by original designation. Synonymy reinstated.

Carmenia Molino-Olmedo, 2001: 85 . Type species Chiasognathus latreillei Solier, 1851 by monotypy. Junior homonym of Carmenia Roewer, 1915 .

Ramirezia Molino-Olmedo, 2002: 124 . Type species Chiasognathus jousellinii Reiche, 1850 by original designation. Junior homonym of Ramirezia Zamponi, 1979 . Mo- lino-Olmedo (2001: 85) attempted to describe this generic name earlier but did not designate a type species, and so the name is not available from the 2001 publication.

Carmeniella Molino-Olmedo, 2003: 29 . Type species Chiasognathus latreillei Solier, 1851 by monotypy. Replacement name for Carmenia Molino-Olmedo 2001 .

Ramireziella Molino-Olmedo, 2003: 29 . Type species Chiasognathus jousellinii Reiche, 1850 by original designation. Replacement name for Ramirezia Molino-Olmedo, 2002 .

Description. Length: 16.6–88.0 mm. Width: 8.4–17.0 mm. Color: Light to dark reddish brown, commonly with green to purple metallic reflections. Head: Form subquadrate to subtriangular, narrower than 1 elytron width, shorter than mandibles in both sexes. Disc surface uneven, often with foveae or apparent tubercles. Surface punctate; punctures fine to coarse, generally setose with short to long setae. Ocular canthus well developed, externally rounded, dividing eye completely into upper and lower portions. Temporal process absent. Anterior angles produced, obtuse or acute. Anterior margin of head in dorsal view varying from weakly emarginate to strongly produced into binodose or acute nasus (nasus when present occasionally migrated anteroventrally and obscured in dorsal view); head below anterior margin and nasus declivous and recessed forming more or less vertical intermandibular projection. Labrum scoop-like, lightly sclerotized, vertical, separated from intermandibular projection by a distinct suture; apex of labrum rounded or acute. Male mandibles 2–6× as long as head, right mandible usually shorter than left, both mandibles with a single, dentate carina (more or less cylindrical, lacking well-defined external or internal carinae present in Sphaenognathus Buquet ); dentate carina generally dorsal at base becoming more internal toward apex. Apex abruptly curved, acute. Mandibular surface punctate; punctures generally setose, setae sparse to dense. Female mandible externally weakly rounded to almost straight in dorsal view, never with external tooth; dorsal surface flattened, internally subdentate (acute tooth occasionally present near middle), punctate; punctures setose with short to long setae. Maxilla and labium with long or short galeal brushes, palps elongate. Mentum transverse, subtrapezoidal, anteriorly emarginate, punctate; punctures fine to coarse, pubescent. Antennal club composed of 6 entirely tomentose antennomeres; antennomeres gradually increasing in length distally. Funicle not tomentose, instead pubescent with scattered setae; distal antennomere of funicle produced as in club or not. Scape elongate, longer than funicle and club together, normally with long setae present at enlarged apex. Pronotum: Shape subtrapezoidal, broadest in basal fifth, anteriorly convergent with rounded sides (margin not strongly produced near anterior angles). Anterior margin sinuate. Anterior angles not prominent. Posterior angle and lateral angle variably developed: obsolete, subdentate, to strongly dentate. Lateral margins distinct and crenulate, rarely obsolete anterolaterally. Dorsal surface generally with variably developed longitudinal and transverse ridges surrounding longitudinal, median furrow; when present ridges less punctate than disc; punctures fine to moderate, variably dense, setose; setae short to long. Each side with subcircular fovea; fovea generally impunctate and glabrous. Scutellum: Form broad, rounded. Surface densely to sparsely punctate; punctures setose or not. Elytra: Form broad and short, convex. Surface gener- ally smooth, occasionally weakly wrinkled, punctate; punctures fine and extremely dense (distance between punctures ≤1 puncture diameter), setose; setae scale-like, microscopic to clearly visible. Humeri broadly rounded. Apex broadly rounded, angulate, or dentate. Epipleuron strongly concave or flat. Wings: Fully developed. Legs: Protibiae dentate or serrate externally from base to 2 larger, apical teeth; ventral surface along internal margin with series of downward-pointing teeth. Mesotibiae and metatibiae with 4–6 external teeth, teeth of metatibiae less distinct, occasionally absent. Onychium of claws with more than 4 setae. Venter: Ventral surface densely pubescent, especially mesosternum. Last abdominal segment distinctly emarginate in males. Male genitalia: Genital capsule simple and parameres of generalized lucanid form. Median lobe strongly sclerotized, form cylindrical or widening apically, with everted internal sac forming flagellum; flagellum simple, length varying from <1 mm to 18 mm (Figs 3–9).

Distribution. Chiasognathus species are distributed in Regions VII-XI and XIV of Chile and in adjacent parts of Argentina.

Diagnosis. In the New World lucanine fauna, Chiasognathus species are immediately recognizable as members of the tribe Chiasognathini because their antennal club is composed of six antennomeres; they are the only stag beetles in southern South America to display this character.

Remarks. The following characters were used by Moxey (1962) to distinguish Chiasognathus from the only other genus of South American Chiasognathini , Sphaenognathus (including the subgenus Chiasognathinus Didier ): front of head projected (nasus) and usually acute, antennal scape 1.5–3.0 times longer than funicle and club combined, and elytral surface not strongly sculptured. Molino-Olmedo (2001) rightfully questioned each of these characters given the variability of the nasus and elytral sculpture and lack of a demonstrable difference in antennal scape length. However, we feel the recognition of these genera as distinct is warranted, and this is especially true with respect to the biogeography of South America, as all known southern South American lucanids are distinct from their Neotropical relatives at the generic level ( Paulsen and Mondaca 2006; Grossi and Paulsen 2009).

There are few reliably expressed characters that can be used to distinguish Chiasognathus and Sphaenognathus , and these unfortunately tend to be observable in only one sex or the other. Male mandibles in Chiasognathus species are rounded externally, not carinate, and therefore appear to be more cylindrical than the mandibles of males of Sphaenognathus species, which are often more triangular in cross section. Importantly,the teeth on Chiasognathus male mandibles are located where the usually toothless (rarely with a single large tooth basally) dorsal carina is found in Sphaenognathus species; the teeth on Sphaenognathus male mandibles are on an internal ventral carina that is not present in Chiasognathus species. Female mandibles are weakly rounded externally in Chiasognathus species, never with an external tooth as in females of some Sphaenognathus species. Male abdominal apices are strongly emarginate in Chiasognathus species but more or less straight or rarely weakly emarginate in Sphaenognathus species. Finally the lateral margin of the pronotum is produced near the anterior angles in females of Sphaenognathus species but is more convergent towards the head in Chiasognathus species females.

Chalumeau and Brochier (2007) emphasized three characters used to differentiate Bomansodus in their earlier work ( Chalumeau and Brochier 1995): male mandibular structure, nasus/intermandibular projection, and effaced lateral pronotal margin. We can find no clear discussion of how the mandibular structure of C. impubis differs from its congeners in either work, and our examination of the mandibles indicates that they are of the same basic plan as those of the remaining Chiasognathus species. Only C. grantii and C. mniszechii more or less consistently possess a prominent nasus; therefore, its absence cannot be used to segregate C. impubis from the genus as a whole. Finally, some specimens of C. impubis we have studied do have a distinct lateral pronotal margin. While it is true that the pronotum is overall more rounded and less distinctly ridged in C. impubis , the character is too weak and variable to support a generic distinction. This is especially true with respect to the shared characters of C. impubis and C. mniszechii , namely the strikingly concave epipleuron, similar protibiae, and beaded elytral margin. For these reasons, we reconfirm the synonymy of Bomansodus with Chiasognathus .

Molino-Olmedo (2001, 2006) accepted (but later rejected) Bomansodus and created additional subgenera with the result of placing almost all species in their own genus or subgenus. There is little justification for such over-splitting of a small, clearly related group based on what amount to species-level characters. We agree with the arguments presented by Chalumeau and Brochier (2007) against the validity of the Molino-Olmedo subgenera. Our greatest concern is that the work was premature given that it was not preceded by a careful revision of the group and was, therefore, founded on an incomplete understanding of the taxonomy of the genus. Thus, we include the seven species in a single genus and are confident that our taxonomic treatment of the species will provide a foundation for future research into the relationships and evolution of Chiasognathus .