Coelambus Thomson, 1860

Fery, Hans, 2017, A new classification of the tribe Hygrotini Portevin, 1929 (Coleoptera: Dytiscidae: Hydroporinae), Zootaxa 4317 (3), pp. 499-529 : 518-521

Subgenus Coelambus Thomson, 1860

Type species: Dytiscus confluens Fabricius, 1787: 193 , by subsequent designation of Zaitzev (1953: 129).

The subgenus Coelambus contains eight Palaearctic and one Nearctic species ( Hygrotus (C.) punctilineatus (Fall, 1919)) .

Diagnosis. Body shape moderately to elongate oval (TL/MW ca. 1.7–2.0); small to medium sized species (TL 3.0– 4.5 mm) (see Fig. 9 for H. (Coelambus) confluens ). Head with anterior clypeal margin truncate and slightly emarginated, border not produced forwards; bead absent. Antennomeres simple, not broadened. Elytra with margin in lateral view strongly ascending to shoulder (see Fig. 54 for H. (Coelambus) caspius (Wehncke, 1875)) ; epipleuron comparably narrow, narrower than mesotibia distally; carina meeting inner margin of epipleuron forming a comparably wide angle (<ca. 150°; similar to Fig. 51 ). Elytra light yellowish (more yellowish brown in H. (Coelambus) ahmeti Hájek, Fery & Erman, 2005 ), distinctly vittate (in some species/individuals vittae strongly reduced in anterior half). Venter usually black, but females of some species (e.g. H. (Coelambus) pallidulus ) with abdomen at least in part yellow or brownish. Last abdominal ventrite without deep depression.

Aedeagus with median lobe elongate, very slender (distal half very thin in lateral view), symmetric or almost symmetric (e.g. in H. (Coelambus) enneagrammus (Ahrens, 1833) , and H. (Coelambus) confluens ; see Figs 23 and 24 ). Parameres with condylar process rather long and forming an almost right angle with distal part ( Figs. 37 and 38 for H. (Coelambus) enneagrammus and H. (Coelambus) confluens , respectively). Male metatarsal claws of equal length.

Distribution. Mainly Palaearctic, with one species in Canada and northern USA ( Hygrotus (Coelambus) punctilineatus ).

Main habitat types. The subgenus includes species typical of both lentic and lotic habitats, with varied salinity tolerance going from freshwater to hypersaline.

Figures

FIGURES 7 – 12. Habitus of: (7) Clemnius (Cyclopius) acaroides, (8) Hygrotus (s. str.) inaequalis, (9) Hygrotus (Coelambus) confluens, (10) Clemnius. (s. str.) decoratus, (11) Clemnius (s. str.) laccophilinus and (12) Clemnius (s. str.) berneri (male holotype and labels).

FIGURES 49 – 55. (49 – 53): Epipleuron with oblique epipleural carina and genicular fossa of: (49) Clemnius (s. str.) berneri, (50) Hygrotus (Leptolambus) polonicus polonicus, (51) H. (Coelambus) caspius, (52) H. (Leptolambus) impressopunctatus and (53) Rhithrodytes agnus; epipleural carina (c) and inner margin of epipleuron (m) including angle mentioned in diagnoses of subgenera. (54 – 55): Elytral margin in lateral view of: (54) H. (Coelambus) caspius (strongly ascending to shoulder) and (55) Clemnius (s. str.) berneri (moderately ascending to shoulder) (Figs 52 and 53 are reproduced from Fery 2013 and from Fery 2016 with the permissions of F. Gusenleitner, Linz, Austria, and G. Foster, Ayr, UK, respectively).

FIGURES 19 – 28. Median lobe in ventral and lateral view of: (19) Clemnius (Cyclopius) acaroides, (20) Clemnius (s. str.) berneri, (21) Clemnius (s. str.) decoratus, (22) Hygrotus (s. str.) inaequalis, (23) H. (Coelambus) enneagrammus, (24) H. (Coelambus) confluens, (25) H. (Leptolambus) parallellogrammus, (26) H. (Leptolambus) impressopunctatus, (27) H. (s. str.) guineensis and (28) H. (Hyphoporus) tonkinensis (Fig. 28 is a modified reproduction of figs 3 and 4 in Brancucci & Biström 2013).

FIGURES 29 – 40. Left paramere of: (29) Clemnius (Cyclopius) acaroides, (30) Clemnius (s. str.) berneri, (31) Clemnius (s. str.) decoratus, (32) Hygrotus (s. str.) inaequalis, (33) H. (Leptolambus) fresnedai, (34) H. (Leptolambus) impressopunctatus, (35) H. (Leptolambus) parallellogrammus, (36) H. (Leptolambus) nubilus, (37) H. (Coelambus) enneagrammus, (38) H. (Coelambus) confluens, (39) H. (s. str.) guineensis and (40) H. (Hyphoporus) tonkinensis (Fig. 40 is a modified reproduction of fig. 5 in Brancucci & Biström 2013).