Hygrotini Portevin, 1929 : 180

Fery, Hans, 2017, A new classification of the tribe Hygrotini Portevin, 1929 (Coleoptera: Dytiscidae: Hydroporinae), Zootaxa 4317 (3), pp. 499-529 : 502-503

Tribe Hygrotini Portevin, 1929: 180 , as tribe of subfamily Hydroporinae .

Type genus: Hygrotus Stephens, 1828: 38 .

Diagnosis. Within Hydroporinae , species of Hygrotini are usually characterised by the following combination of characters:

- metepisternum (metepiventrite in Miller & Bergsten 2016: 139) reaching mesocoXal cavities, not separated by mesepimeron (in contrast to members of Vatellini );

- apices of elytra and last abdominal ventrite not acuminate (in contrast to members of Methlini );

- prosternal process elongate with apeX narrowly pointed or rounded (in contrast to members of Hydrovatini );

- dorsal (anterior) margin of metafemur separated from metacoXal lobe by metatrochanter (in contrast to members of Laccornellini and Laccornini );

- humeral portion of epipleuron with oblique carina delimiting genicular fossa (character shared with members of Hydrovatini , Hyphydrini and genus Rhithrodytes Bameul, 1989 in Hydroporini ; cf. Fery 2013, 2016; see Fig. 53 for Rhithrodytes agnus Foster, 1992 , and Figs 49–52 for some Hygrotus species).

- metatarsal claws equal in length, with eXception of members of C. saginatus -group (see Fery 1992, 1995, 2003) and in contrast to members of Hyphydrini and Pachydrini (see e.g. Pederzani 1995; Miller & Bergsten 2016).

None of these characters is, however, an unambiguous synapomorphy of the group. We introduce here a potentially unambiguous synapomorphy of tribe Hygrotini , recognised by one of us (H.F.). In many members of Hydroporinae the antennal cavities in the fronto-lateral part of the head are rather deep and more or less conical (much flatter e.g. in Hyphydrini ), allowing the movement of the first antennomere (the scape). These cavities are delimited dorsally by the anterior border of the clypeus ("b" in Figs 3–6 ). Inside each cavity there is a capsule in which the base of the scape (the condyle) is articulated. This capsule is delimited by a distinct more or less circular carina ("a" in Figs 3–6 ). In all studied species of Hygrotini there is an additional–more or less semicircular–carina ("c" in Figs 4–6 ) which is closer to the border of the clypeus and surrounds in part the other carina. In the species of Hydroporini this additional carina is not present (see Fig. 3 for Hydroporus dorsalis ( Fabricius, 1787) or fig. 33 in Fery & Bouzid 2016 for Tassilodytes parisii (Gridelli, 1939)). In a few species of Hygrotini the second carina is difficult to observe or is very narrow (as in e.g. Heroceras descarpentriesi and Hygrotus (Coelambus) salinarius ), but is nevertheless clearly perceptible when the specimens are properly illuminated and orientated. However, in most specimens studied of Hygrotus (Coelambus) masculinus (Crotch, 1874) , the second carina is reduced to a short piece near the mandible.

According to the phylogeny reconstructed in Villastrigo et al. (in press) the tribe Hygrotini is divided into two well supported monophyletic lineages, which are considered here with generic rank. Each of these two lineages is in turn divided into generally well supported clades, which are treated as subgenera. In some cases these clades have lower support in the molecular phylogeny, and are also not well defined morphologically (see below and AppendiX for a discussion on the clypeal bead, the main character used so far to differentiate genera and subgenera within Hygrotini ), so we opted for a subgeneric rather than a generic rank.

Due to the new classification 67 species are for the first time included in the genus Clemnius n. gen. or in Hygrotus , thus their names becoming new combinations. We have listed all these species in Table 1 marked with " n. comb. " These changes have also generated some homonymies which will be resolved in a separate work (H. Fery, manuscript in preparation).

The genera and subgenera are treated below in the same order as in Fig. 2 , starting from the lower part of the figure.

Figures

FIGURE 2. Dendrogram showing the new classification of Hygrotini. A number of species without molecular data (no voucher number) have been inserted near morphologically similar species with molecular data. Acronyms refer to biogeographical regions.

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 3 – 4. Antennal cavities of: (3) Hydroporus dorsalis (Hydroporini) and (4) Hygrotus (Leptolambus) lagari (Fery, 1992) (a: carina delimiting capsule for scape; b: fronto-lateral border of clypeus; c: second carina).

FIGURES 5 – 6. SEM micrographs with details of head and antennal cavities of: (5) Hygrotus (Leptolambus) impressopunctatus (frontal view) and (6) Hygrotus (s. str.) inaequalis (oblique ventral view) (a, b and c as in Figs 3 – 4; d: clypeal stripe; e: labrum).