Hydrochus xingu, Perkins, 2021

Perkins, Philip D., 2021, Taxonomy of water beetles in the genus Hydrochus Leach, 1817, from Bolivia, Brazil and Paraguay (Coleoptera: Hydrochidae), Zootaxa 4994 (1), pp. 1-93 : 13-15

H. xingu species group

Figs. 1 , 3 , 5 , 43 , 44 , 46, 47 , 55 , 57 , 67 , 70

Members of the H. xingu species group are recognized by the combination of the following characteristics: 1) small size, ca. 1.75–2.75 mm; 2) male genitalia lacking parameres; 3) basal piece elongate and very slender, usually marked arcuate in lateral view; 4) distal piece elongate, slender, sometimes with minute processes distally. There is considerable variation in the habitus sculpture and color, for example comparing the very different H. xingu and H. longissimus ( Figs. 44 , 46 ). Some species have costate elytral interseries, some species do not. Currently, six species are recognized: H. constrictus , H. longissimus , H. obliquus ( Peru) , H. pietersenae , H. tripartitus ( Peru) , and H. xingu .

Remarks. Makhan (1998, 2001) proposed several new genera in the Hydrochidae . Hansen (1999), Short & Hebauer (2006), and Short & Fikáček (2011) have considered these to be invalid, and have placed them in synonymy with Hydrochus . Based on the male genitalia, it appears that species in the H. xingu species group are related to species placed in one of Makhan’s “genera”. The taxonomy of the very diverse genus Hydrochus would benefit from a comprehensive molecular phylogenetic study. Until such time, the following statement from Hansen (1999) seems to hold true: “Hence, there seems to be no justification for considering [Makhan’s “genera”] as distinct genera … there is certainly no phylogenetic support for generic rank (this would almost inevitably leave Hydrochus as paraphyletic).”

Neotropical Hydrochus species distributions

Many of the species found in the study area of this contribution, Bolivia, Brazil, and Paraguay, are present in two or three of the countries. One of the principal reasons for these shared distributions is the Pantanal, known as one of the world’s largest wetlands, which occupies areas of all three countries ( Figs. 54 , 64 ). However, the portion of the Pantanal in Brazil is huge compared to that in Bolivia and Paraguay. Shared distributions in the study area include the following: Present in all three countries (12 species); present in Bolivia and Brazil, but not Paraguay (7 species); present in Brazil and Paraguay, but not Bolivia (8 species); present in Bolivia and Paraguay, but not Brazil (0 species);

Species that are known from only one of the three countries are overwhelmingly Brazilian, as would be expected based on the much larger size, greater topographic diversity, and the resulting greater ecosystems diversity of the country. In the study area the following numbers of species are currently known only from one of the three countries: Bolivia (6), Brazil (40), Paraguay (3). The total species for each country are: Bolivia (25); Brazil (67); Paraguay (23).

Many of the species found in the study area are also found in other South American countries. Locality and specimen deposition data have been published for 12 study area species that are also found in Peru ( Perkins 2020c), five also found in Ecuador ( Perkins 2020b), and 17 also found in Venezuela ( Perkins 2019c). Of these, only one species, H. bituberculatus , is found in the study area and all three of the other countries (map, Fig. 58 ); surely this basically reflects the lack of specialized collecting efforts for Hydrochus specimens.

There are two very general distribution patterns for species with wide distributions. In one pattern the distributions go northward from the study area, through the Andes, to Venezuela (e.g., H. bituberculatus , Fig. 58 and H. leei , Fig. 69 ). Rarely, species are only known from eastern Brazil, Ecuador, and Venezuela (e.g., H. bicarinatus , Fig. 56 ). In the other pattern the distributions go northward from the study area, via Central Brazil and the Amazon, to Venezuela.

H. obscurus and H. leei , two very commonly collected species, have the greatest distributional range of Neotropical Hydrochus , being found from Paraguay northward to Mexico ( Figs. 63 , 69 ), with hundreds of published locality records ( Perkins, 2019c, 2020a, 2020c, and 2021). The distribution of H. obscurus goes northward from southern Paraguay, through southern Brazil and the Amazon, to Venezuela, Panama, and is widespread in Central America. Whereas the distribution of H. leei goes northward from southern Paraguay, through western South America, to Venezuela, and is widespread in Central America.

Contrastingly, 28 species in the study area are known only from the type locality (27 Brazil, 1 Bolivia). Although some of these species might truly be very rare endemics, most of the very rare records certainly reflect the lack of specialized collecting efforts in the many marshes, swamps, roadside ditches, and other wetlands in the study area .

Revisions, which are now in process, include Argentina, Colombia, French Guiana, Guyana, and Suriname. Consequently, distribution maps given herein that do not have localities marked in those countries reflect the unpublished status, not necessarily the absence of species.

The Hydrochus species distributions published by D. Makhan are very problematic. For example, Worthington, et al. (2016) placed into synonymy five species of North American Hydrochus that Makhan had erroneously described as new. These taxonomic changes of course change the known distributions of the senior synonyms. Also, as would be expected, an author that creates so many synonyms also misidentifies other, non-type specimens (some of which have been encountered in the current revisionary studies), and these misidentifications appear in his papers. Any errors of distributions published by Makhan before the publication of Hansen’s (1999) Hydrophiloidea catalog will of course be found therein as supposedly valid distribution records. These records are not reliable, and should be ignored until the identifications can be verified, or corrected. However, as has been noted by Worthington, et al. many of the specimens these problematic distributions are based on cannot be found or obtained, hence making verification impossible at this time. Another serious problem results from the fact that some holotypes of Makhan species, which had been dissected by him, before being borrowed by the current author, do not have the crucial male genitalia with the specimen. The only Makhan distribution records that can be reasonably considered valid at this time are those of the holotypes of species that have been found to be valid species by subsequent authors.

The problem of invalid species distributions of Neotropical Hydrochus was increased by the work of Oliva (1996), who synonymized 16 Makhan South American species, unfortunately using inadequate and inaccurate work on the pivotal male genitalia morphology ( Perkins, 2019a, c). These inaccuracies also result in misidentifications and the resulting incorrect distribution records. Again, verifying or correcting identifications of non-types is rendered impossible at this time because specimens cannot be obtained. Only revisionary studies can provide reliable species distribution records of American Hydrochus .

For background on the taxonomic and nomenclatural problems peculiar to Neotropical Hydrochus , especially as they pertain to the publications of D. Makhan (1992, 1993, 1994, 1995a, b, 1996, 1998, 2000, 2001, 2004a, 2004b, 2005), the reader is referred to Oliva (2000), Jäch (2006), Short & Hebauer (2006), Worthington et al. (2016), and Perkins (2019a, c; 2020a, b).

New Species Descriptions

Figures

FIGURE 1. Dorsal habitus of Hydrochus species in study area.

FIGURE 3. Dorsal habitus of Hydrochus species in study area.

FIGURE 5. Dorsal habitus of Hydrochus species in study area.

FIGURE 63. Geographical distribution of H. obscurus.

FIGURE 64. Geographical distribution of H. tarsalis.

FIGURE 69. Geographical distribution of H. leei.

FIGURE 70. Pictorial aid to species groups of Hydrochus from Bolivia, Brazil and Paraguay, using male genitalia. Not to same scale.

FIGURES 42–43. Habitus and male genitalia. 42. Hydrochus astrictus Perkins. 43. Hydrochus pietersenae Makhan.

FIGURES 44–45. Habitus and male genitalia of holotypes. 44. Hydrochus longissimus n. sp. 45. Hydrochus casuarius n. sp.

FIGURES 46–47. Habitus and male genitalia of holotypes. 46. Hydrochus xingu n. sp. 47. Hydrochus constrictus n. sp.

FIGURES 55–56. Geographical distributions. 55. Endemics and near endemics. 56. H. bicarinatus and H. merkli.

FIGURES 57–58. Geographical distributions. 57. Endemics and near endemics. 58. H. bituberculatus.

FIGURES 67–68. Geographical distributions. 67. H. argutus species group. 68. H. cracentis.

FIGURES 53–54. Geographical distributions. 53. H spanglerorum species group. 54. H collaris species group.