Phaenostoma stochasma, Gustafson & Short & Aezs, 2010

Gustafson, Grey T. & Short, Andrew E. Z., 2010, Redescription of the Neotropical water scavenger beetle genus Phaenostoma (Coleoptera: Hydrophilidae) with description of two new species, Acta Entomologica Musei Nationalis Pragae (suppl.) 50 (2), pp. 459-469 : 466-468

Phaenostoma stochasma sp. nov.

( Figs. 2C , 4 C–D)

Type locality. Costa Rica: Cartago Province, Turrialba, Barbilla National Park.

Type material. HOLOTYPE: ♁, ‘COSTA RICA. Prov. Cartago, / Turrialba, P.N. Barbilla, Camino al Rio / Dantas. 300m. 22 OCT 2000.W./ Arana, Mantillo. L _N_596893_217500/ #60877’, ‘[barcode]/INB0003116831 / INBIOCRI COSTA RICA’ ( INBio) . PARATYPES (5 exs.). COSTA RICA: CARTAGO PROVINCE: Turrialba, Barbilla National Park, Finca Topoyiyo, 600m, 17.xi.2000, leg. W. Arana, Mantillo (1 ♀, KSEM). GUANACASTE PROVINCE: Pitilla Station, 9 km S. Santa Cecilia, 700m, 6–18.viii.1993, leg. P. Rios (1 ♀, INBio). LIMON PROVINCE: Sector Cerro Cocoi, Farm of E. Rojas, 150m, (31.i)–(21.ii).1992, leg. E. Rojas (1 ♀, INBio). ALAJUELA PROVINCE: Upata, Sector Sapote, 625 m, 20.x.2001, leg. A. Lopez, trampa de Mantillo (1 ex., INBio). VENEZUELA: AMAZONAS STATE: Tobogan de la Selva, 7.i.2006, leg. A. Short, AS-06-017 (1 ♁, MIZA).

Diagnosis. Body size 2.8–3.0 mm. Body form weakly convex with elytra apically weakly explanate. Process of the mesoventrite with constriction at suture with metaventrite; suture and form as in Fig. 2C . Aedeagus as in Fig. 4 C–D.

Phaenostoma stochasma sp. nov. is distinguished from P. posticatum by its smaller size and comparatively weakly convex body and weakly explanate elytra apically. It is similar to Phaenostoma kontax sp.nov. but can be easily distinguished by its larger size, aedeagus with parameres not strongly curved inward apically, as well as the shape of its sternal process. The anterior hood of the process of the mesoventrite of P. stochasma sp. nov. is often on the same plane as the rest of the process, unlike P. kontax sp. nov. in which the anterior hood is located above the plane of the sternal process.

Description. Color. Dorsal surface appearing reddish brown to brown. Elytral and pronotal discs often appearing darker in color than lateral and apical margins. Head often appearing darker than the rest of the body. Ventral surface dark brown to reddish brown. Legs often lighter brown to reddish brown. Tarsi and palps and antennae yellow.

Head. Punctation fine with the average distance between punctures ca. 3–4× the diameter of one puncture.

Thorax. Pronotal punctation fine with greatest distance between punctures ca. 4–5× the diameter of one puncture. Elytral punctation coarse (and weakly impressed) with the average distance punctures ca. 1–2× the diameter of one puncture. Elytral margins apically weakly explanate. Process of the mesoventrite broad and constricted at suture with metaventrite ( Fig. 2C ), with apical hood thickly bordered and frequently appearing on the same level as mesosternal process plane in lateral view.

Abdomen. Aedeagus with parameres straight along outer margin, slightly curved inward at apex. Median lobe almost reaching apex of parameres ( Fig. 4C, D ).

Etymology. Stochasma is a Greek word meaning an arrow or aimed spear, referring to the spear-shaped process of the metaventrite that is held forward as if aimed. Treated as noun in apposition.

Distribution. Known from Costa Rica and Venezuela.

Remarks. All six known specimens of this species are from different collecting events (indeed, four provinces are represented by the five Costa Rican specimens). While the specimens from Costa Rica and Venezuela are very geographically and ecologically distant, we were not able to find any substantive morphological differences between them, including the aedeagus. We suspect the species is more broadly distributed.

Figures

Fig. 2. Sternal process of Phaenostoma species. A – P. kontax sp. nov.; B – P. posticatum (Sharp, 1887); C – P. stochasma sp. nov.

Fig. 4. Aedeagi of Phaenostoma species. A – P. posticatum (Sharp, 1887) (Costa Rica); B – P. kontax sp. nov. (holotype); C – P. stochasma sp. nov. (holotype; Costa Rica); D – P. stochasma sp. nov. (paratype; Venezuela). Scale bar = 0.2 mm.