Phaenostoma d’Orchymont, 1937

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 : 461-463

Phaenostoma d’Orchymont, 1937

Phaenostoma d’Orchymont 1937: 133 . Gender: neuter.

Type species. Cyclonotum posticatum Sharp, 1887 (original designation).

Diagnosis. Small to medium sized beetles. Size 2.1–3.7 mm. Body form broadly oval and strongly convex. Antennae with nine antennomeres, including a three-segmented, loose pubescent club. Clypeus broad and expanded to cover labrum, truncate to subtruncate apically. Elytron without striae except for a sutural stria appearing in posterior third of the elytron and continuing to the apex. Elytra slightly explanate in posterior half. Prosternum narrow, not carinate medially. Process of the mesoventrite linear, forming a composite structure with the raised portion of the metaventrite. First metatarsomere longer than second. Tarsi with brush of setae ventrally.

In the New World, there is no other genus of the tribe that possesses an elytral sutural stria and no other elytral striae. Other coelostomatine genera either have no striae at all (e.g., Phaenonotum Sharp, 1882 , Galapagodacnum d’Orchymont, 1937 , Lachnodacnum d’Orchymont, 1937 ) or multiple rows of elytral striae in addition to the sutural one (e.g., Dactylosternum Wollaston, 1854 , Cyclotypus Sharp, 1882 , Badioglobus Short, 2005 ). In dorsal habitus, the genus is most similar to the common genus Phaenonotum , and is often confused with it in collections.

Redescription. Head. Clypeus large and expanded to conceal labrum, weakly convex, and truncate to subtruncate apically. Ground punctation present. Eyes well developed, weakly convex, and separated by 4–5 times the diameter of one eye. Eyes constricted medially by anterior and posterior emargination. Frontoclypeal suture usually appearing absent. Antennae with 9 antennomeres, ca. 3/4 × as long as the width of the head; antennomeres 7–9 densely pubescent and forming a loose club. Club length ca. 4 × the width of the apical segment. Maxillary palps bearing four palpomeres, with palpomeres 2 and 4 similar in size and both slightly longer than palpomere 3. Palpomeres 3 and 4 with sides nearly symmetrical. Stipes laterally with long fine yellow setae. Labial palps bearing three palpomeres; palpomere 3 much longer than 1 & 2 combined. Palpomeres 2 and 3 bearing long setae. Mentum length ca. half the width, depressed anteromedially, pubescent. Gula constricted medially, forming an elongate triangle anteriad and a more obtuse triangle posteriad.

Thorax. Pronotum convex, often meeting seamlessly in outline with elytra; broadened posteriorly meeting elytral margins; pronotal ground punctation often more weakly impressed than that on the elytra. Pronotal marginal bead well developed laterally, becoming shallower anteromedially. Scutellum punctate; forming an equilateral triangle. Elytral striae absent except for a sharp sutural stria arising in the posterior one-third and continuing to apex; ground punctation often well impressed and dissimilar to pronotal punctation; marginal bead well developed. Prosternum small and flat. Mesoventrite with a well-developed, raised linear process; angular, anteriorly proceeded by an elevated sub-parallel ridge that reaches posteriad to meet elevated process of the metaventirte. Metaventrite very sparsely pubescent; elevated medially along entire length, beginning low and broad posteriad and becoming more narrow, elevated, and subparallel anteriad as it meets the posteriad portion of the mesoventral ridge process. The process arises anteriad to the metacoxae and proceeds between the mesocoxae. Pro- and metacoxae narrowly separated. Mesocoxae separated the process of the mesoventrite. Mesocoxae large and extending the width of the mesoventrite. Metacoxae flattened, extending the width of the metaventrite. Profemora densely pubescent basally on both dorsal and ventral surfaces; meso- and metafemora glabrous with a few isolated setae along anterior margin. Femora and tibiae noticeably flattened dorso-ventrally. Femora with tibial grooves developd throughout the posterior margin. Tibia spinose with larger spines apically. Tarsi with moderately dense setal brush ventrally. First metatarsomere longer than second. Tarsal claws relatively small and moderately curved.

Abdomen. Abdomen with 5 ventrites, bearing dense, short pubescence throughout. Ventrite 5 rounded posteriorly, without apical emargination and larger than preceding segments. The aedeagus trilobed ( Fig. 4 ) with the phallobase ca. 1/4 the length of the rest of the aedeagus. Aedeagus with parameres having lateral margins thickened and ventral inner margins thin.

Biology. Most specimens with collecting data were sifted from forest litter (many P. posticatum and some P. kontax sp. nov.), berleses of ‘flower falls’ (some P. kontax sp. nov.) or taken at flight intercept traps (some P. posticatum ). The single Venezuelan specimen was taken along the riparian corridor at Tobogan de la Selva, likely in an aquatic or water-saturated situation.

Remarks. SHARP (1887) originally described what is now P. posticatum in the genus Cyclonotum Erichson, 1837 (now a synonym of Coelostoma Brulle,1835 ). Generic concepts of coelostomatine genera were poorly differentiated at the time (and still are in many cases), and members of Cyclonotum are now distributed in at least five contemporary genera: Coelostoma , Phaenostoma , Phaenonotum , Lachnodacnum , and Dactylosternum . Indeed, P. posticatum was transferred between three genera ( Cyclonotum , Dactylosternum , and Coelostoma ) before d’ORCHYMONT (1937) erected Phaenostoma for the species based on the following combination of characters: presence of a sutural stria, but lack of other elytral striae, moderately dense ventral setal tufts on the tarsi, and a fused, linear, elongate sternal process.

Figures

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.