Chasmogenus Sharp, 1882

Giron, Jennifer C. & Short, Andrew Edward Z., 2018, Three new genera of acidocerine water scavenger beetles from tropical South America (Coleoptera, Hydrophilidae, Acidocerinae), ZooKeys 768, pp. 113-158 : 146-147

Chasmogenus Sharp, 1882

Chasmogenus Sharp, 1882: 72.

Dieroxenus Spangler, 1979: 753. Syn. n.

Discussion.

In comparing the new taxa described here to existing genera, we observed striking similarities between the monotypic Andean genus Dieroxenus Spangler and the widespread genus Chasmogenus Sharp. Dieroxenus shares most diagnostic characters of New World Chasmogenus , including general body size, the presence of sutural striae (extremely rare in Acidocerinae ), antennae with eight antennomeres, a longitudinal carina on the mesoventrite, and a “simple” tri-lobed aedeagus ( Hebauer 1992). It does differ from Chasmogenus in a few respects: Dieroxenus has a slightly more robust body form, slightly shorter maxillary palps, and its elytral systematic punctures are enlarged and easily distinguished from the ground punctation. However, most if not all of these features could be attributed to the unusual seep-inhabiting nature of this species, while other Chasmogenus are known from streams and marshes. Additionally and perhaps most convincing morphologically, is that the aedeagal form of Dieroxenus (Fig. 21E ) matches that of some Neotropical Chasmogenus (e.g., see Figs 1 - 4 in Short 2005).

When Dieroxenus was described nearly 40 years ago, the systematics and classification of the Hydrophilidae was radically different. Chasmogenus was then considered part of Helochares , and most genera that are now in the Acidocerinae were assigned to different tribes than they are today. Consequently, Spangler (1979) did not consider what we now call Chasmogenus when making his comparisons, and instead focused on its similarities and differences from Enochrus , which we now know is not very closely related ( Short and Fikáček 2013).

Figures

Figure 1. Habitus of Crucisternum spp.: A-D Crucisternum escalera: A dorsal view B lateral view C ventral view D head E-H Crucisternum queneyi: E dorsal view F lateral view G ventral view H head. Scale bars: 1 mm.

Figure 4. Thorax and abdomen of Crucisternum ouboteri: A ventral view of mesoventrite (white arrow pointing longitudinal carina and transverse ridge); B posterior view of metafurca: (at) anterior tendon, (c) crux, (ds) dorsal sheath, (fa) furcal arm, (h) hemiductus, (ls) lateral sheath, (s) stalk; C fifth abdominal ventrite.

Figure 21. Habitus of Chasmogenus cremnobates: A dorsal view B lateral view C ventral view D head E aedeagus. Scale bar 1 mm.