Cercyon, OF

Suzumura, Alyssa Lee, Kobayashi, Norio & Ôhara, Masahiro, 2019, Revision of the Beach-Dwelling Species of Cercyon Leach (Coleoptera: Hydrophilidae) of the West Coast of North America, The Coleopterists Bulletin 73 (3), pp. 473-493 : 475-476

KEY TO THE SPECIES OF ADULT MARINE CERCYON OF WESTERN COASTAL NORTH AMERICA

1. Dorsal surface of head, pronotum, and elytra completely without microsculpture; male with a patch of dense, felt-like setae covering mentum ( Fig. 8C ); size large, length over 3.5 mm; male genitalia as in Fig. 7D–F ...... ........................................ C. dux Sharp

1 ʹ. At least head with distinct, though sometimes fine microsculpture; mentum with at most sparse setae, without felt-like patch of setae; smaller, usually not exceeding 4.0 mm in length ................................................ 2

2. Pronotum with dense, distinct microsculpture, at least on lateral portions ( Fig. 12D ); posterior portion of elytra sparsely pubescent ( Fig. 12G ); very small, less than 2.8 mm in length; male genitalia as in Fig. 7M–O . ...... ................................. C. setulosus Sharp

2 ʹ. Pronotum without apparent microsculpture except sometimes in a small area behind anterior angles ( Figs. 5D , 10D ); elytra lacking pubescence; larger, more than 2.8 mm in length ................................................ 3

3. Elytral striae deeply impressed, particularly at base where 1 st 2 often seem to connect ( Fig. 9A ); elytral intervals convex; mesoventral plate diamond-shaped ( Fig. 9E, F ); male genitalia as in Fig.7G–I ........................... ...................... C. fimbriatus Mannerheim

3 ʹ. Elytral striae rather superficial, 1 st 2 striae not seemingly connected; elytral intervals flat; mesoventral tablet long and narrow ( Figs. 5E, F , 10E, F ) ........................................... 4

4. Pronotum piceous, elytra uniformly piceous to testaceous or fulvous ( Fig. 1G ), sometimes with darkened crescentic spot in apical 1/3; small area behind apical angles of pronotum with microsculpture ( Fig. 10D ); apices of parameres widened, as in Fig. 7J ............... .......................... C. luniger Mannerheim

4 ʹ. Pronotum and elytra piceous to testaceous, irregularly lightened at margins ( Fig. 1A ); pronotum completely without apparent microsculpture ( Fig. 5D ); apices of parameres narrow, as in Fig. 7A .................................. ....... C. whuljensis Suzumura , new species

Figures

Fig. 8. Cercyon dux, male (WA16AS-015). A) Habitus, oblique view, B) Head, oblique view, C) Head, ventral view, showing adhesion discs, D) Basal portion of left elytron, E) Prosternum and meso- and metaventrites, ventral view, F) Pro- and mesoventrites, oblique ventral view.

Fig. 7. Cercyon species, male genitalia (parameres and basal piece, median lobe, and ninth ventrite, respectively). A–C) C. whuljensis (BC14MO-025), D–F) C. dux (BC14MO-030), G–I) C. fimbriatus (BC16MO-033), J–L) C. luniger (WA18AS-008), M–O) C. setulosus (WA16AS-006). Bp = basal piece; Co = corona; Ed = ejaculatory duct; Pm = parameres. Scale bars = 0.5 mm.

Fig. 12. Cercyon setulosus, male (WA16AS-006). A) Habitus, oblique view, B) Head, oblique view, C) Head, ventral view, showing adhesion discs, D) Left half of pronotum, E) Prosternum and meso- and metaventrites, ventral view, F) Prosternum and mesoventrites, oblique ventral view, G) Apical half of right elytron, oblique posterior view.

Fig. 5. Cercyon whuljensis, male (BC14MO-008). A) Habitus, oblique view, B) Head, oblique view, C) Head, ventral view, showing adhesion discs, D) Right anterolateral region of pronotum, E) Prosternum and meso- and metaventrites, ventral view, F) Prosternum and mesoventrites, oblique ventral view.

Fig. 10. Cercyon luniger, male (WA18AS-008). A) Habitus, oblique view, B) Head, oblique view, C) Head, ventral view, showing adhesion discs, D) Right anterolateral region of pronotum, E) Prosternum and meso- and metaventrites, ventral view, F) Prosternum and mesoventrites, oblique ventral view.

Fig. 9. Cercyon fimbriatus, male (BC16MO-033). A) Habitus, oblique view, B) Head, oblique view, C) Head, ventral view, showing adhesion discs, D) Basal portion of right elytron, E) Prosternum and meso- and metaventrites, ventral view, F) Prosternum and mesoventrites, oblique ventral view.

Fig. 1. Cercyon species, dorsal and lateral habitus, respectively. A, B) C. whuljensis (WA18AS-008), C, D) C. dux (WA16AS-015), E, F) C. fimbriatus (WA17AS-004), G, H) C. luniger (WA17AS-008), I, J) C. setulosus (BC16MO-032).