Hydrodessus J. Balfour-Browne, 1953

Miller, Kelly B., 2016, Revision of the Neotropical diving beetle genus Hydrodessus J. Balfour-Browne, 1953 (Coleoptera, Dytiscidae, Hydroporinae, Bidessini), ZooKeys 580, pp. 45-124 : 50-54

Taxon classification Animalia Coleoptera Dytiscidae

Hydrodessus J. Balfour-Browne, 1953 Figs 1-7, 8-10, 11-13, 14-16, 17-19, 20-22, 23-25, 26-28, 29-31, 32-34, 35-41, 42-47, 48-51

Hydrodessus J. Balfour-Browne, 1953: 55 (type species: Hydrodessus siolii J.Balfour-Browne, 1953: 56 by original designation); Young 1967: 80, 83; 1969: 2; Biström 1988: 36; Nilsson 2001: 236, 2013: 214.

Brinckius Guignot, 1957: 38 (type species: Brinckius biguttatus Guignot, 1957: 39 by original designation); Biström 1988: 37; Nilsson 2001: 236, 2013: 214; synonymy by Young 1969: 2.

Brinkius , Young 1967: 80, 83; 1969: 2 (incorrect subsequent spelling).

Diagnosis.

Hydrodessus are distinguishable from other Bidessini by the following combination: 1) the lateral lobes of the aedeagus comprised of a single segment (instead of two or three), 2) without basal pronotal striae, and 3) without prominent carinae on the disc of elytron and no large pores on dorsal and ventral surfaces. In addition, Hydrodessus do not have basal elytral striae, modifications to the anterior clypeal margin (except in one species), a transverse occipital line between the posterior margins of the eyes, nor a transverse carinae across the elytral epipleuron at the humeral angle.

Natural history.

Relatively little is know of the natural history of most members of the group. A great many museum specimens were collected at lights. Other specimens were collected from forest streams, often in low numbers. Occasionally, longer series have been found in tropical forest streams. Larvae and other aspects of their natural history have not been described.

Taxonomic history.

Hydrodessus has a complicated character combination, and because of this has had a history of ambiguous taxonomic placement. The genus was early placed in or near Bidessini , but not without reservation ( Guignot 1957). Though Young (1967; 1969) classified it in Bidessini , Biström (1988) restricted the definition of that tribe to those Hydroporinae with bi- or trisegmented lateral lobes, which are single-segmented in Hydrodessus (and at least some Amarodytes ( Benetti and Régil Cueto 2004)). Hydrodessus was subsequently placed incerta sedis with respect to tribe until Miller and Bergsten (2014) placed it back into Bidessini . This was based on a large phylogenetic analysis including many DNA sequence data and morphology which resulted in Hydrodessus together with Peschetius (previously placed in Bidessini by Miller et al. (2006)) and some Amarodytes in a clade, and this sister to other Bidessini . Miller et al. (2006) expanded the definition of Bidessini to include taxa with 1) a spermathecal spine, and 2) five lobes on the crusher teeth of the proventriculus, which resulted in Peschetius and Amarodytes included in the tribe, but Hydrodessus was not examined comprehensively at that time. Based on evidence gathered for this revision, at least some Hydrodessus have a spermathecal spine, though not all do, and some have five-lobed crusher teeth on the proventriculus, though not all were examined. Based on this, and on evidence from Miller and Bergsten (2014), the genus is recognized here in Bidessini , and related to Peschetius and (at least) some Amarodytes .

The first species of Hydrodessus , Hydrodessus siolii J. Balfour-Browne, was described along with the genus description ( Balfour-Browne 1953). Subsequent to this, Guignot (1957) erected the new genus, Brinckius Guignot, with four new species. Spangler (1966) added two new species from Peru to Hydrodessus . In his treatment of the genera of New World Bidessini , Young (1967) was uncertain whether to synonymize Brinckius with Hydrodessus , though he keyed them out together. Nilsson (2001) regarded the synonymy of Brinckius with Hydrodessus to date to Young’s (1967) paper. However, Young (1967, 83) seemed to make it clear at that time that he could not “…decide… whether Brinkius [sic] of Guignot should be accorded recognition." Even so, he soon ( Young 1969) did synonymize Brinckius with Hydrodessus and provided a list of the included species. He then ( Young 1970) added two more and provided a key to all the species. The next contribution was by Spangler (1985), who added five new species from Guyana and also provided a key to the species. Though not included in his concept of Bidessini , Biström (1988) listed the species. The last addition of species to the genus was three by Makhan (1994), bringing the total to 17 valid Hydrodessus species prior to this revision.

Monophyly of Hydrodessus as deliminated here has not been demonstrated, and all the known diagnostic features described here for the genus are plesiomorphies. Other distinctive characters (potential synapomorphies) are variable within the genus. Many species have a lateral carina on the elytron extending posteriorly from the humeral angle, but not all do, and some of those that do have it only weakly developed. Most also have longitudinal carinae on the metaventrite approximately continuous with the metacoxal lines, but not all do. These two characters are also not always in the same combinations. All species have a similar overall appearance, robust, laterally discontinuous between the pronotum and elytron, elongate, with a variety of color patterns, and a somewhat characteristic shape for the prosternal and metasternal processes, but these are not particularly convincing as synapomorphies. Future research should concentrate on carefully examining the monophyly of the group and its relationships with Amarodytes and Peschetius , and possibly some Hypodessus Guignot, as well. It seems likely that Hydrodessus may eventually need division into multiple genera.

Distribution.

Hydrodessus are characteristic mainly of northern South America from Ecuador and Peru to Brazil. The greatest known density of species is from southern Venezuela to Suriname. There are a few species extending south to Paraguay.

Key to the species of Hydrodessus

Two species, Hydrodessus amazonensis and Hydrodessus nanayensis , are problematic since no specimens were examined (the types were not found). Hydrodessus nanayensis is included in the key since, based on previous work, it appears to be very similar to (if not identical with) Hydrodessus siolii . The other species, Hydrodessus amazonensis , is not easily keyed with the characters included here since many of the states important for the key are not described for that species. It is included in the species treatments, however, and the male genitalia are relatively distinctive and diagnostic.