Helochares (Hydrobaticus), MacLeay, 1871: 131

Short, Andrew Edward Z. & Girón, Jennifer C., 2018, Review of the Helochares (Hydrobaticus) MacLeay of the New World (Coleoptera: Hydrophilidae: Acidocerinae), Zootaxa 4407 (1), pp. 29-50 : 33-34

Hydrobaticus MacLeay, 1871: 131 .

Diagnosis. Among New World Acidocerinae , species of Hydrobaticus can be distinguished by the following combination of characters: (1) antennae with 9 antennomeres, (2) fifth ventrite with a distinct apicomedial emargination lined with coarse setae, (3) mesoventrite without a distinctly elevated keel or protuberance, (4) elytra with ten rows of serial punctures (except H. championi , H. laevis , and H. politus ), and (5) aedeagus with parameres simple and fused, forming a tube-like structure, with median lobe appearing as a flat, tongue-like strap ( Figs 7 , 8 ). It should be emphasized that these characters will only separate species of the New World species, and are not sufficient to distinguish Hydrobaticus from species of other subgenera in other parts of the world.

Description. Body size: 4.2–7.0 mm. Head. Antennae with nine antennomeres, including three-segmented pubescent club. Maxillary palps curved inward and moderate in length, generally subequal to slightly longer in length to the width of head just anterior to eyes; inner face of palpomere 2 slightly curved; apical palpomere subequal in length to slightly shorter than penultimate. Labial palps short, distinctly shorter than mentum width. Mentum slightly concave centrally, strongly emarginated anteromedially; surface moderately to strongly sculptured; appearing mostly glabrous to possessing a few scattered short setae. Frons with series of irregular systematic, setae-bearing punctures anterior to each eye. Systematic punctures also present on clypeus and labrum but often blend with ground punctation, though occasionally appearing distinct. Eyes not or only slightly bulging, continuous with outline of the head or nearly so; not emarginated anteriorly by the frons. Thorax. Pronotum with systematic punctation in lateral thirds, each puncture usually bearing a short seta. Prosternum moderately wide, tectiform medially and usually with a narrow, fine longitudinal carina; very slightly elevated in anterior third. Mesoventrite with a low, weakly elevated bulge, never with an elevated keel, lamina, or tubercle. Metaventrite without a glabrous patch posteromedially, or at most with two small glabrous spots situated adjacent to midline in posterior quarter. Elytra with ten rows of very coarse serial punctures (except H. championi , H. laevis , and H. politus ) which may or may not be depressed into grooves on at least the posterior half of the elytra. Procoxae set with sparse setae, but without thickened spines. Hind femora densely pubescent except on distal fifth–sixth or less. All tarsi with five tarsomeres. Abdomen. With five pubescent ventrites, density of setae ranging from sparse to very dense. Fifth ventrite distinctly emarginated apicomedially, emargination set with thickened setae. Aedeagus ( Figs. 7–8 ) 2.0 to 2.8-times longer than its widest point, with basal piece short, nearly one third the length of parameres; parameres basally fused together into a dorsoventrally flattened tube with basal margin rounded to mesally notched; lateral outer margins of parameres slightly sinuate, parallel along basal half or third, continuing nearly parallel to apically diverging; widest point of aedeagus usually near apex of parameres; widest point of each paramere narrower than median lobe; median lobe with lateral basal apodemes, nearly as long as median lobe; gonopore situated on distal half of median lobe.

Remarks. As previously mentioned, characters used to define the subgenus as a whole do not seem to demarcate natural groups of species. The diagnosis that is provided here should be used to separate Nearctic and Neotropical members of Hydrobaticus only, though some of these features are common to the subgenus in other regions.

Figures

FIGURE 7. Aedeagi of Helochares (Hydrobaticus) spp. (A) H. trujillo n. sp., (B) H. zamora n. sp., (C) H. maculicollis (Florida), (D) H. maculicollis (Kansas), (E) H. maculicollis (Pennsylvania), (F) H. nexus n. sp. (Venezuela), (G) H. nexus n. sp. (Panama), (H) H. nexus n. sp. (Ecuador), (I) H. politus n. sp., (J) H. laevis n. sp., (K) H. championi.

FIGURE 8. Aedeagi of Helochares (Hydrobaticus) normatus. (A) Oregon, (B) California, (C) Arizona, (D) Mexico, (E) Costa Rica.