Phaenostoma posticatum ( Sharp, 1887 )

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 : 465-466

Phaenostoma posticatum ( Sharp, 1887)

( Figs. 1 , 2B , 4A )

Cyclonotum posticatum Sharp, 1887: 769

Dactylosternum posticatum (Sharp) : ZAITZEV (1908: 402)

Coelostoma posticatum (Sharp) : KNISCH (1924: 113)

Phaenostoma posticatum (Sharp) : d’ORCHYMONT (1937: 133)

Type locality. Panama: Chiriqui Province, Bugaba.

Type material examined. SYNTYPE 1: ‘ Cyclonotum / posticatum / Ind. Typ D.S. / Bugaba Champion [on same card as specimen]’, ‘Sharp Coll. / 1905.-313.’, ‘Bugaba, / Panama. / Champion.’, ‘B.C.A. Coll. I. 2. / Cyclonotum / posticatum, / Sharp.’ (sex undetermined) ( BMNH). SYNTYPE 2: ‘ Cyclonotum / posticatum / Type. D.S. [on same card as specimen]’, ‘Bugaba, / Panama. / Champion.’, ‘Sharp Coll. / 1905.-313.’, ‘B.C.A. Coll. I. 2. / Cyclonotum / posticatum, / Sharp.’, ‘Type [red disc, upside down]’, ‘ ♀ ’ ( BMNH). No lectotype was designated.

Additional material examined (60 exs.). COSTA RICA: PUNTARENAS PROVINCE: Osa Peninsula, Foundation Neotropical , 10 km W. Rincon, 180 m 08º42 ′ 30 ″ N 83º31 ′ 30 ″ W, 22.vi.1997, leg. R. Anderson, ridge forest litter, RSA 1997-026C (1 ex., CMNC) ; same data except 21.vi.1997, RSA 1997-024B (2 exs., CMNC) ; same data except 200 m, 24.vi.2001, lowland forest litter, 2001-120B (3 exs., CMNC) ; Osa Peninsula , 4 km W. Rancho Quemado, 08º42 ′ 30 ″ N 83º35 ′ 33 ″ W, 500 m, 24.vi.2001, leg. R. Anderson, ridge forest litter, 2001-121A (1 ex., CMNC) ; Osa Peninsula, Rancho Quemado , 200 m, iv.1992, leg. K. Flores (2 exs., INBio) ; same data except 10 –31.iii.1992, leg. A. Marin (1 ex., INBio) ; same data except 1–21.xii.1992, leg. A. Marin (1 ex., INBio) ; same data except vii.1992, leg. M. Segura (2 exs., INBio) ; same data except xii.1992, leg. F. Quesada (1 ex., INBio) ; Golfito, Agujas Station , 250–350 m, 10.x.1990, leg. A. Azofeifa, Berlese trap (2 exs., INBio) ; Golfito, Agujas Station, Sendero Bonanza , Bosque Primero , 300 m, 11.viii.2000, leg. A. Azofeifa, Mantillo (1 ex., INBio) . LIMON PROVINCE: Sector Cerro Cocori, Farm of E. Rojas, 150 m, iii.1993, leg. E. Rojas (1 ex., INBio) ; same data except iv.1993 (4 exs., INBio) ; same data except x.1991 (4 exs., INBio) ; same data except ix.1991 (4 exs., INBio) ; same data except vi.1991 (3 exs., INBio) ; same data except iii.1992 (1 ex., INBio) ; same data except viii.1991 (2 exs., INBio) ; same data except iv.1992 (2 exs., INBio) ; same data except viii.1992 (1 ex., INBio) ; Sector Cocori , 30 km N of Cariari, 100 m, xii.1993, leg. E. Rojas (1 ex., INBio) . GUANACASTE PROVINCE: Pitilla Station , 9 km S. Santa Cecilia, 700 m, 22.viii.1993, leg. C. Moraga (2 exs., INBio) ; same data except 6–18.viii.1993, leg. P. Rios (5 exs., INBio, NMPC) ; same data except 3–18.x.1991, leg. P. Rios (3 ex., INBio) ; same data except iii.1995 (4 exs., INBio) ; same data except 19.v.–3.vi.1993 (1 ex., INBio) ; same data except viii.1991, leg. C. Moraga (1 ex., INBio) ; same data except i.1994 (2 ex., INBio) ; same data except x.1994 (2 exs., INBio) . HEREDIA PROVINCE: 16 km S.S.E. La Virgen, 1070 m, 10º16 ′ N 84º05 ′ W, 10–21.iv.2001, INBio-OET-ALAS transect (1 ex., INBio) .

Diagnosis. Body size 3.1–3.7 mm. Body form strongly convex, hemispherical. Process of the mesoventrite as in Fig. 2B , aedeagus as in Fig. 4A . Aedeagus with parameres parallel sided for ca. basal ¾ of the length and angled inward in apical ¼.

Phaenostoma posticatum is the largest of the described species in the genus, always greater than 3.0 mm in length. It can also readily be distinguished from its congeners by the overall shape of its sternal process: the hood of the process has well developed margins and the hood appears above the rest of the plane of the sternal process. Its aedeagus is also distinct, with strongly sinuate outer margins at the apex of the parameres.

Description. Color. Dorsal surface dark brown (sometimes appearing black) to reddish brown. Lateral margins of elytra and pronotum often paler in color. Elytra apically with a region of paler coloration. Pronotal margins with a lateral band of pale coloration often ranging to yellow in color. Head usually darker than pronotum and elytra. Ventral surface dark brown with legs tending to be lighter in coloration and appearing reddish brown to yellowish. Antennae, palps, tarsi, and tarsal setae yellow.

Head. Ground punctation fine with average distance between punctures approximately 4× the diameter of one puncture.

Thorax. Pronotal punctation extremely fine with average distance between punctures ca. 4–5× the diameter of a puncture. Elytral punctation weakly impressed and coarser than the pronotal and head punctation. Apical margins of elytra not explanate. Average distance between punctures of the elytra ca. 3× the diameter of one puncture. Impression of the elytral punctation shallow and depressions appearing uneven in size. Process of the mesoventrite as in Fig 2B ; with apical hood distinctly bordered and frequently appearing above the plane of the rest of the sternal process in lateral view. Process of the mesoventrite with margins nearly parallel and not constricted at suture with metaventrite.

Abdomen. Aedeagus ( Fig. 4A ) with parameres parallel-sided for ca. basal ¾ their total length with apical ¼ angled inward. Apex of median lobe not reaching the apex of the parameres.

Distribution. Recorded from Costa Rica, Panama, Brazil, and Peru. Only Costa Rican and Panaman specimens were examined for this work and the occurrence of this species cannot be therefore confirmed for South America.

Remarks. Costa Rican specimens were taken by sifting forest litter, Malaise traps and flight intercept traps. We are not aware of any specimens being taken in an aquatic situation, despite extensive aquatic sampling by the second author and others in Costa Rica, suggesting the species has a terrestrial way of life.

Figures

Fig. 1. Dorsal and ventral habitus of Phaenostoma posticatum (Sharp, 1887) (Costa Rica). Scale bar = 1.0 mm.

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.