Cercyon (Cercyon) unipunctatus (Linnaeus, 1758)

Ryndevich, Sergey K., Jia, Fenglong & Fikáček, Martin, 2017, A review of the Asian species of the Cercyon unipunctatus group (Coleoptera: Hydrophilidae: Sphaeridiinae), Acta Entomologica Musei Nationalis Pragae (Acta. Ent. Mus. Natl. Pragae) 57 (2), pp. 535-576 : 537-569

publication ID

https://doi.org/ 10.1515/aemnp-2017-0089

publication LSID

lsid:zoobank.org:pub:A472A777-7FF5-4305-98DE-1F1AC73E8433

DOI

https://doi.org/10.5281/zenodo.5335094

persistent identifier

https://treatment.plazi.org/id/03D7C933-8B11-DE7C-6E8C-FBB94335FA3D

treatment provided by

Marcus

scientific name

Cercyon (Cercyon) unipunctatus
status

 

Cercyon (Cercyon) unipunctatus View in CoL group

Diagnosis. Body elongate oval, length 1.8–3.8 mm, width 0.9–1.9 mm; dorsal surface convex without microsculpture; head black, pronotum pale with central dark spot, or dark with pale lateral margins; elytron pale (yellow, reddish or brownish), in some species with dark sutural interval or dark spot on elytral disc, rarely dark coloration prevailing (resulting in seemingly dark elytra with pale spots in C. kabaki and dark form of C. unipunctatus ); maxillary palps pale (yellowish); mesoventral plate narrowly elongate, 3.3–11.0× as long as wide; metaventrite without femoral lines.

Comparison with other species groups in Cercyon s. str. The pale maxillary palpi and absence of femoral lines of the metaventrite diagnose members of C. unipunctatus group from C. haemorrhoidalis species group (femoral lines present, palpi dark), C. nigriceps group (femoral lines present), C. marinus and C. obsoletus groups (maxillary palps dark) and from C. berlovi Shatrovskiy, 1999 (maxillary palpi dark). The dorsal coloration of the members of C. unipunctatus group is never unicolored, it always has at least the head and parts of the pronotum darker than the elytra; in this they differ from C. olibrus Sharp, 1874 and C. rotundulus Sharp, 1884 (dorsally unicolored), C. borealis Baranowski, 1985 (pronotum and elytra concoloured) and C. cultriformis Wu & Pu, 1995 (head pale dorsally). The dorsal surface of head, pronotum and elytra is always smooth, lacking any microsculpture; this diagnoses the C. unipunctatus group from the C. dux group, C. algarum group, C. tristis group, C. sericatus Hebauer, 2002 and C. emarginatus Baranowski, 1985 . The body is never compressed and the tibiae are not distinctly widened distally and armoured by stout blunt spines; this distinguishes the C. unipunctatus group from C. depressus Stephens, 1829 and related species. See Discussion for a more detailed comparison with similar species ( C. ovillus Motschulsky, 1860 and C. lateralis (Marsham, 1802) etc.).

List of species of the Cercyon unipunctatus group

C. divisus Hebauer, 2002

China (Yunnan, Sichuan), Nepal, India.

C. flavimarginatus sp. nov.

China (Yunnan).

C. kabaki Ryndevich, 2004

China (Sichuan).

C. kubani sp. nov.

China (Yunnan).

C. limbatus Mannerheim, 1842

Not occurring in Asia. Other regions: Western coast of Northern America.

C. quisquilius (Linnaeus, 1760)

China (Gansu, Guangxi, Henan, Inner Mongolia, Jiangxi, Qinghai, Shaanxi, Shanghai, Sichuan, Yunnan), Cyprus, Iran, Israel, Japan, Kazakhstan, Kyrgyzstan, Mongolia, Nepal, Russia (Western and Eastern Siberia, Far East), Saudi Arabia (north), Syria, Tajikistan, Turkey, Turkmenistan, Uzbekistan. Other regions: Europe, North Africa, North America, Caribbean (introduced), Australia (introduced), South America (introduced), Hawaii (introduced).

C. undulipennis sp. nov.

China (Sichuan,? Yunnan)

C. unipunctatus ( Linnaeus, 1758)

Kazakhstan, Russia (Western and Eastern Siberia, Far East), China (Heilongjiang), Japan. Other regions: Europe, North America.

C. unipustulatus Nakane, 1982

Japan, Russia (Far East).

C. verus Shatrovskiy, 1989

Russia (Far East,?Western Siberia).

Key to Asian species of the C. unipunctatus group

1(4) Elytra with very apparent sparse long semi-erect yellowish pubescence at least laterally (may be broken dorsally; Figs 5A,B View Fig , 6A View Fig in lateral view). Elytral intervals weakly but distinctly convex ( Figs 5A,B View Fig , 6A View Fig ). Elytra uniformly yellowish or reddish or slightly darker on elytral disc, but without distinct central dark spot or dark sutural interval. Mesoventral plate very narrow (8–11× longer than wide; Figs 5G View Fig , 6F View Fig ).

2(3) Lateral margins of pronotum narrowly pale ( Fig. 6A View Fig ) Sutural interval of elytra not darker than general elytral coloration. Intervals of elytra slightly convex in medial and apical parts. Median lobe of the aedeagus evenly wide throughout, strongly narrowing at extreme apex ( Fig. 6C View Fig ). ........................... Cercyon undulipennis View in CoL sp. nov.

3(2) Lateral margins of pronotum very widely pale ( Figs 5A–B View Fig ). Sutural interval of elytra darker than general elytral coloration. Intervals of elytra very slightly convex only in apical part. Median lobe of the aedeagus widest at midlength, very strongly narrowing in apical half ( Fig. 5D View Fig ). ................................................ Cercyon kubani View in CoL sp. nov.

4(1) Elytra without pubescence, or at most with short very inconspicuous pubescence at lateral-most parts. Elytral intervals flat, if weakly convex then elytra with very distinct black central spot. Elytra uniformly yellow or with very distinct black patterns, even darker specimens with a set of pale spots. Mesoventral plate wider (at most 6× longer than wide).

5(6) Elytra largely black, with characteristic pattern of pale spots, or yellow with black and dark brown spots, forming a characteristic pattern ( Figs 4A–B View Fig ). Median lobe of the aedeagus narrow with very long apex ( Fig. 4D View Fig ). ................................................... ............................................................................... Cercyon kabaki Ryndevich, 2004 View in CoL

6(5) Elytra largely yellowish of reddish, if larger black areas are present they form a central dark spot, leaving apical and lateral portions widely pale ( Figs 1 View Fig , 3A View Fig , 7A View Fig , 8A View Fig , 9A View Fig , 10A–B View Fig , 11–12 View Fig View Fig ). Median lobe wide throughout, or at least widening at midlength.

7(8) Lateral margins of pronotum very widely pale, dark central pronotal spot may be confined to central area or lobate laterally. Elytra rarely uniformly yellow, usually with dark sutural interval, or with dark spots basally and/or in humeral region, or with combination of these ( Fig. 1 View Fig ). Median lobe without series of setae in apical half, basal apodemes short ( Fig. 2B View Fig ). ........................................ Cercyon divisus Hebauer, 2002 View in CoL

8(7) Lateral margins of pronotum narrowly pale, dark pronotal spot never confined only to central area and never distinctly bilobate laterally ( Figs 3A View Fig , 7A View Fig , 8A View Fig , 9A View Fig , 10A–B View Fig ). Elytra uniformly pale, or with dark sutural interval or more or less small central dark spot, but never with basal or humeral dark spots. Median lobe with series of setae in apical half, basal apodemes long.

9(12) Elytra uniformly pale.

10(11) Elytra and lateral parts of pronotum yellowish, pale lateral part of pronotum less extended ( Fig. 7A View Fig ). Phallobase longer than parameres, median lobe widest subapically ( Figs 7B–C View Fig ). ................................................. Cercyon quisquilius (Linnaeus, 1760) View in CoL

11(10) Elytra and lateral parts of pronotum reddish, pale lateral part of pronotum wide ( Fig. 10B View Fig ). Phallobase ca. as long as parameres, median lobe parallel-sided ( Figs 10C–D View Fig ). ..................................................................... Cercyon verus Shatrovskiy, 1989 View in CoL (part)

12(9) Elytra pale with central dark spot or dark sutural interval ( Figs 3A View Fig , 11–12 View Fig View Fig ).

13(18) Elytra at most with dark sutural interval, without distinct central dark spot.

14(15) Sutural interval nearly completely dark (except at extreme base) ( Fig. 3A View Fig ). Median lobe narrower, without abruptly narrowing apex ( Fig. 3C View Fig ). ........................................ .............................................................................. Cercyon flavimarginatus View in CoL sp. nov.

15(14) Sutural interval usually not completely dark (dark coloration confined to narrow stripe at suture or small central area). If sutural interval nearly completely dark, then median lobe wider, with abruptly narrowing apex ( Figs 8C View Fig , 10D View Fig ).

16(17) Pentagonal area of metaventrite with coarse and dense punctation, distance between the individual punctures in lateral parts ca. 1–3 × their diameters ( Fig. 10F View Fig ). Mentum with distinct dense transverse wrinkles ( Fig. 10I View Fig ). Pale lateral margins of pronotum wider ( Figs 10A–B View Fig ). Coloration of elytra as in Figs 12E–F View Fig . ....................................... ..................................................................... Cercyon verus Shatrovskiy, 1989 View in CoL (part)

17(16) Pentagonal area of metaventrite with shallow and sparse punctation, distance between individual punctures in lateral parts ca. 4–6 × their diameters ( Fig. 8E View Fig ). Mentum with very indistinct transverse wrinkles ( Fig. 8G View Fig ). Pale lateral margins of pronotum narrower ( Fig. 8A View Fig ). Coloration of elytra as in Fig. 11A View Fig . ...................................... .................................................................... C. unipunctatus ( Linnaeus, 1758) View in CoL (part)

18(13) Elytra with distinct central dark spot; spot rounded, triangular or pentagonal in shape.

19(20) Mesoventral plate widely rounded posteriorly, facing a distinct anterior projection of metaventral pentagon ( Fig. 9F View Fig ). Median lobe slightly constricted in apical third ( Fig. 9C View Fig ). Sutural interval of elytra completely dark including basally, elytral central spot always large, reaching at least to one third of elytral interval ( Figs 12A–D View Fig ). ............. ........................................................................ Cercyon unipustulatus Nakane, 1982 View in CoL

20(19) Mesoventral plate sharply pointed posteriorly, anterior part of metaventral pentagon only indistinctly bulged ( Figs 8F View Fig , 10G View Fig ). Median lobe parallel-sided ( Figs 8C View Fig , 10D View Fig ). Sutural interval of elytra usually pale basally. Elytral central spot small (on intervals 1–2 only) to very large ( Figs 11 View Fig , 12E–J View Fig ).

21(22) Pentagonal area of metaventrite with coarse and dense punctation, distance between individual punctures in lateral parts ca. 1–3× their diameters ( Fig. 10F View Fig ). Mentum with distinct dense transverse wrinkles ( Fig. 10I View Fig ). Pale lateral margins of pronotum wider ( Figs 10A–B View Fig ). Coloration of elytra as in Figs 12E–J View Fig . ................................................. ..................................................................... Cercyon verus Shatrovskiy, 1989 View in CoL (part)

22(21) Pentagonal area of metaventrite with shallow and sparse punctation, distance between individual punctures in lateral parts ca. 4–6× their diameters ( Fig. 8E View Fig ). Mentum with with very indistinct transverse wrinkles ( Fig. 8G View Fig ). Pale lateral margins of pronotum narrower ( Fig. 8A View Fig ). Coloration of elytra as in Fig. 11 View Fig . ............................... .................................................................... C. unipunctatus ( Linnaeus, 1758) View in CoL (part)

Kingdom

Animalia

Phylum

Arthropoda

Class

Insecta

Order

Coleoptera

Family

Hydrophilidae

Genus

Cercyon

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