Cercyon castaneipennis sp. n., an overlooked species from Europe (Coleoptera: Hydrophilidae) Author Vorst, Oscar text Zootaxa 2009 2054 59 68 journal article 10.5281/zenodo.186663 8b57f67b-1f57-4d9b-97a6-a0913feb256f 1175-5326 186663 Cercyon castaneipennis Vorst , new species ( Figs. 1 , 3, 5 , 7–9 , 13 ) Diagnosis. A large Cercyon s. str. , very similar to C. obsoletus ( Gyllenhal, 1808 ) with which it has been confused until now. It differs at first glance from this species by the more shining overall appearance, and the usually reddish brown colour of the elytra ( Fig. 1 ). Table 1 summarizes the differences between both species. Description. Body length: 3.50–4.20 mm (median 3.85 mm , N = 20). Elytral length (apex of scutellum to apex of elytra): 2.55–3.05 mm (median 2.85 mm , N = 20). Elytral width: 2.20–2.60 mm (median 2.40 mm , N = 20). Black; elytra usually reddish brown with a large black triangular scutellar macula pointing backwards along the suture and more or less extending along the basal margin and the anterior portion of the lateral margins ( Fig. 3 ). Head, pronotum and elytra with fine and dense punctuation, but somewhat sparser than in C. obsoletus and as a result more shining than in this species. Elytral striae well defined, somewhat more pronounced and slightly deeper impressed than in C. obsoletus , especially in the parascutellar region. Elytra rather wide, slightly more convex than in C. obsoletus , more strongly narrowed posteriorly, lateral margins halfway sublinear over about one third of its length, while regularly curved in C. obsoletus . Lateral margin of elytra immediately behind anterior angle with a tiny transverse plica, as in C. obsoletus . Raised middle portion of mesoventrite narrow (length: width = 4.2–5.3, median 4.7, N = 10), somewhat more slender than in C. obsoletus . Metaventrite without femoral lines. Maxillary palpi and antennae dark piceous to black. Antennal club somewhat more elongate (length: width = 1.8–2.1, median 1.9, N = 10) and as a rule slightly darker than in C. obsoletus ( Fig. 5 ). Mentum with punctuation clearly fused to form transverse wrinkles. Legs piceous to brown, tibia paler than femora, tarsi paler than tibia; in general slightly darker than in C. obsoletus . Male genitalia ( Figs. 7–9 ) similar to that of C. obsoletus , but relative length smaller (aedeagal length: elytral length = 0.36–0.38, median 0.38, N = 6), and relative length of basal piece (BP) less than in C. obsoletus (parameral length: BP length = 0.68–0.75, median 0.72, N = 6). BP with a more extensive asymmetrical emargination basally. Type material. Holotype : 3, "Elst, Plantage Willem III / 164.3-444.0 V3974H / 3.v.2008 / leg. O. Vorst / koemest" ( RMNH ), collected near Elst ( The Netherlands , Province of Utrecht). Paratypes : SWEDEN : Småland: 1 spec., Huskvarnaberget, 30.vii.2002 , S. Snäll ( NMPC ). THE NETHERLANDS : Province of Groningen: 4 spec., Sellingen, 22.vi.2001 , cattle dung in meadow, J. Huijbregts (cJH); Province of Drenthe: 3, Ƥ ( Fig. 1 ), Anderen, Eexterveld, 29.v.2005 , cattle dung in grazed heath land, O. Vorst (cOV); 1 spec., Anloo, Westerholt, 2.ix.2000 , dung of large herbivores in meadow, J. Huijbregts (cJH); 3, Ƥ, Balooërveld, 29.v.2005 , pony dung in meadow, J. Huijbregts (cJH); Ƥ, Uffelte, Oosterzand, 26.viii.2006 , cattle dung in grazed heath land, O. Vorst (cOV); Province of Overijssel: 3, Ƥ, Springendal, 14.vi.2003 , horse dung in meadow in forest, J. Huijbregts (cJH); Province of Gelderland: 3 33, 3 ƤƤ, De Imbosch, Nieuwe Kamp, 20.v.2008 , cattle dung in meadow, O. Vorst (cOV); Province of Utrecht: Ƥ, 2 spec., Austerlitz, Traayweg, 16.iv.2007 , horse dung in mixed forest, O. Vorst (cOV); 2 33, 5 ƤƤ, 1 spec., Elst, Plantage Willem III, 3.v.2008 , cattle dung in meadow, O. Vorst ( 2 33, 5 ƤƤ), F. van Nunen (1 spec.) (cFN, cOV, RMNH , ZMAN ); Province of Noord-Holland: 1 spec., Amsterdam, Amsterdamsche Bosch, 8.v.2004 , F. van Nunen (cFN); Province of Noord-Brabant: Ƥ, Biesbosch, Aakvlaai, 8.iv.2008 , cattle dung in meadow, O. Vorst (cOV); 3 ƤƤ, Biesbosch, Lange Plaat, 10.v.2008 (Ƥ), 17.ix.2008 (2 ƤƤ), horse dung in meadow, O. Vorst (cOV). CZECH REPUBLIC : Jihočeský kraj: 4 spec., Kvilda, 23.vii.2003 , Z. Švec (cZS); Hlavní mĕsto Praha: 1 spec., Praha, Kosoř, 25.vi.2003 , S. Snäll (cSS); Zlínský kraj: 1 spec., Halenkov, 17.vii.1983 , J. Vitner (cJV). SLOVAKIA : Košický kraj: 1 spec., Plešivecká Planina, 18.viii.1985 , cattle dung, J. Vitner (cJV); 2 spec., Silická Brezová, 21.v.1986 , cattle dung, J. Vitner (cJV); 2 spec., Turňa [nad Bodvou], 18.vii.1985 , Sejkora ( NMPC ); 1 spec., Zádiel, 25.iv.1986 , cattle dung, J. Vitner (cJV); Žilinský kraj: 2 spec., Pribylina, 19.vii.1998 , A. Bieńkowski (cAB); 13, Turček, 23.vii.1991 , Martinová & Znamenáček ( NMPC ). POLAND : Warmińsko-Mazurskie: 2 spec., Pelnik, 16.v.1996 , A. Bieńkowski (cAB). LATVIA : Tukums District: 1 spec., Klapkalnciens, 15.vi.2005 , coastal refuse on the beach, O. Vorst (cOV). TABLE 1. Diagnostic characters separating Cercyon castaneipennis and C. obsoletus .

C. castaneipennis	C. obsoletus
punctuation of upper side	fine, somewhat sparser (Fig. 1)	fine, somewhat denser (Fig. 2)
elytral striae	well defined, somewhat more pronounced, especially in the parascutellar region (Fig. 1)	poorly defined, inner striae almost obsolete anteriorly (Fig. 2)
elytral colouration	usually reddish brown with a large black triangular scutellar macula (Fig. 3)	usually piceous black, paler towards the apex, apical fifth usually reddish brown (Fig. 4)
antennal club	somewhat more elongate (Fig. 5), as a rule darker	somewhat less elongate (Fig. 6), as a rule paler
punctuation of mentum	fused to form transverse wrinkles	clearly separated, not or only to very limited extent fused

FIGURES 3–6. Elytral colour pattern and antennae of Cercyon castaneipennis (3, 5) and C. obsoletus (4, 6). 3–4. Elytral colour pattern, scale bar 0.5 mm; 5–6. Antenna, scale bar 0.2 mm. Distribution. Currently known from Central Europe ( The Netherlands , Czech Republic , Slovakia and Poland ) and the southern part of North Europe ( Sweden and Latvia ) ( Fig. 13 ). Bionomics. All but one specimen were collected from dung of large herbivores as cattle and horse, in both open and enclosed habitats. The single Latvian specimen collected from coastal refuse on the beach probably was astray. Specimens were collected from April through September. Etymology. The specific epithet is an adjective derived from the Latin castaneus [chestnut coloured] and penna [wing], referring to the chestnut coloured elytra. Remarks. The name Cercyon obsoletus a. rubridorsis Reitter, 1909 was proposed for a colour form with the elytra “rot, eine dreieckige gemeinschaftliche Basalmakel an der Naht, die Basis schmal, die S[eiten] vorne länger schwarz gefärbt” [red, a common triangular basal macula along the suture, the basis narrow, the sides anteriorly more extensive black]. This is actually an accurate description of C. castaneipennis , to which it might refer. As an infrasubspecific name it is however not available (Art. 45.5, 45.6, ICZN 1999 ). There are no other names available that could potentially be applied to the new species ( vide infra ).