Cercyon, LEACH, 1817

Angus, Robert B, Sadílek, David, Shaarawi, Fatma, Dollimore, Hayley, Liu, Hsing-Che, Seidel, Matthias, Sýkora, Vít & Fikáček, Martin, 2021, Karyotypes of water scavenger beetles (Coleoptera: Hydrophilidae): new data and review of published records, Zoological Journal of the Linnean Society 192 (3), pp. 958-958 : 958-

publication ID	https://doi.org/ 10.1093/zoolinnean/zlaa105
persistent identifier	https://treatment.plazi.org/id/356287D9-FF84-AF2B-4CE1-FE5DFDB56EBC
treatment provided by	Felipe
scientific name	Cercyon
status

Treatment

GENUS CERCYON LEACH, 1817 View in CoL

( FIGS 16-17 View Figure 16 View Figure 17 )

Material examined: Cercyon (Dicyrtocercyon) ustulatus (Preyssler, 1790) : 1 male ( BMNH): United Kingdom, Surrey, Egham , R. Angus lgt .

Cercyon (Paracercyon) analis (Paykull, 1798) : 1 female ( NMPC): Czech Republic, Bohemia. Černíky , 3.vi.2019, collecting in compost, V. Sýkora lgt .

Cercyon convexiusculus Stephens, 1829: 1 male, 1 female (BMNH): United Kingdom, Norfolk, East Walton, R. Angus lgt. 1 spec. (NMPC): Czech Republic, Zliv GoogleMaps , 49.0794131°N 14.3895733°E, 24.iv.2019, V. Kolá ř lgt.

Cercyon sternalis (Sharp, 1890) : 2 females ( BMNH): United Kingdom, Norfolk, East Walton , R. Angus lgt .

Cercyon tristis (Illiger, 1801) : 1 female ( BMNH): United Kingdom, Norfolk, East Walton , R. Angus lgt .

Cercyon marinus Thomson, 1853: 1 View in CoL male (BMNH): United Kingdom, Norfolk, East Walton , R. Angus lgt.

Cercyon impressus (Sturm, 1807) View in CoL : 2 males ( BMNH): United Kingdom, Surrey, Egham , R. Angus lgt .

Cercyon obsoletus (Gyllenhal, 1808) : 1 male ( BMNH): United Kingdom, Surrey, Bookham Common, R. Angus & H. Gray lgt .

Cercyon lateralis (Marsham, 1802) : 1 male ( BMNH): United Kingdom, Windsor, Boveney , R. Angus & H. Gray lgt .; 1 male ( BMNH): United Kingdom, Windsor, Windsor Deer Park , R. Angus & H. Gray lgt .

Cercyon haemorrhoidalis (Fabricius, 1775) : 1 male (B M N H): U n i t e d K i n g d o m, Wi n d s o r, B o v e n e y, R. Angus & H. Gray lgt .; 2 males ( BMNH): United Kingdom, Windsor, Windsor Deer Park, R. Angus & H. Gray lgt .

Cercyon melanocephalus (Linnaeus, 1758) : 1 male, 1 female ( BMNH): United Kingdom, Windsor, Windsor Deer Park, R. Angus & H. Gray lgt .

Karyotypes: The examination of the eleven species shown here indicates that the subgenus Dicyrtocercyon (with the only species Cercyon ustulatus ; Fig. 16A View Figure 16 ) and C. convexiusculus of the Cercyon convexiusculus group ( Fig. 16F–I View Figure 16 ) have the karyotype of 2 n = 28 + Xy (♂). All nine remaining species ( Cercyon sternalis and Cercyon tristis of the Cercyon convexiusculus group, Cercyon analis of the subgenus Paracercyon and other examined ‘usual’ European Cercyon ) have the karyotype 2 n = 22 + Xy (♂).

Cercyon ustulatus ( Fig. 16A View Figure 16 ) has a large metacentric X chromosome, about the same size as autosome 6. The autosomes are a mixture of metacentric and subacrocentric ones, with pair 14 about a quarter of the length of pair 1.

Cercyon convexiusculus ( Fig. 16F–I View Figure 16 ) has a small metacentric X chromosome about the same size as autosome pair 9. Autosome pairs 4, 10 and 12–14 are acrocentric to subacrocentric whereas the remaining pairs are metacentric to submetacentric. Interestingly, pair 1 is polymorphic for a pericentric inversion— the East Walton specimens are either homozygous acrocentric ( Fig. 16F View Figure 16 ) or heterozygous ( Fig. 16G, H View Figure 16 ) whereas the Czech specimen ( Fig. 16I View Figure 16 ) is homozygous submetacentric.

The remaining species differ from each other in the relative length of the X chromosome: it is a long metacentric in Cercyon lateralis ( Fig. 17B–E View Figure 17 ), Cercyon haemorrhoidalis ( Fig. 17I–K View Figure 17 ) and Cercyon melanocephalus ( Fig. 17L–N View Figure 17 ), and shorter but still metacentric in Cercyon marinus ( Fig. 17A View Figure 17 ), Cercyon obsoletus ( Fig. 17F, G View Figure 17 ) and Cercyon impressus ( Fig. 17H View Figure 17 ). The X chromosome cannot be identified in Cercyon analis ( Fig. 16B View Figure 16 ), Cercyon tristis ( Fig. 16C View Figure 16 ) and Cercyon sternalis ( Fig. 16D, E View Figure 16 ) because only females are available.

Note: The yet unpublished DNA-based molecular phylogeny of the Megasternini (Arriaga-Varela & Fikáček, unpubl.) revealed that the genus is polyphyletic. The groups used in Figures 16 View Figure 16 and 17 View Figure 17 correspond to these molecular findings, each of them represents a monophyletic DNA clade.