Ephydrolithus, Girón & Short, 2019

Giron, Jennifer C. & Short, Andrew Edward Z., 2019, Three additional new genera of acidocerine water scavenger beetles from the Guiana and Brazilian Shield regions of South America (Coleoptera, Hydrophilidae, Acidocerinae), ZooKeys 855, pp. 109-154 : 120-125

Ephydrolithus gen. nov. Figs 5 , 6 , 7 , 8 , 9

Type species.

Ephydrolithus hamadae sp. nov.

Differential diagnosis.

Small beetles (1.8-3.3 mm), oval in dorsal view, moderate to strongly convex in lateral view (e.g., Figs 5B , 6F ), yellowish brown to dark brown. Antennae with nine antennomeres (e.g., Fig. 6C ). Maxillary palps short (e.g., nearly two thirds the width of the head) and stout (e.g., Fig. 6H ). Elytra without sutural striae, and only rarely with impressed striae (e.g., Ephydrolithus ogmos ); ground punctures sharply marked, uniformly and rather densely distributed; systematic punctures slightly larger and deeper than remainder punctures; serial punctures usually absent (present but reduced in E. ogmos ). Prosternum flat (e.g., Figs 5C , 6C ), sometimes only slightly elevated along longitudinal midline. Posterior elevation of mesoventrite usually with a transverse ridge (Fig. 7A ; except in E. ogmos and E. spiculatus which bear a well-developed tooth, e.g. Fig. 6C ). Metaventrite densely pubescent, except for a large median teardrop-shaped glabrous patch. Posterior femora glabrous for the most part, with few scattered setae along basal half to basal two thirds, with hydrofuge pubescence along anterodorsal margin; well-developed tibial grooves, sometimes covered by hydrofuge pubescence. Fifth abdominal ventrite apically truncate, with stout setae (e.g., Fig. 7C ).

Among Neotropical acidocerines, Ephydrolithus has a general resemblance to Katasophistes (see Girón and Short 2018), especially by characters of the elytral punctation, which exhibits five rows of deep/large systematic punctures. Ephydrolithus can be easily recognized from Katasophistes by the mostly glabrous metafemora, with only few scattered setae on anterior surface, as opposed to at most glabrous along apical third in Katasophistes . Ephydrolithus might also resemble some species of Chasmogenus ; nevertheless, the absence of sutural striae in Ephydrolithus allows its recognition.

Ephydrolithus can be distinguished from other Neotropical acidocerines with mostly glabrous metafemora such as Quadriops (e.g. Girón and Short 2017) by the entire (as opposed to divided) eyes. From Tobochares (e.g. Kohlenberg and Short 2017) Ephydrolithus can be distinguished by the number of antennomeres (nine in Ephydrolithus , eight in Tobochares ). In addition, in some species of Ephydrolithus the tibial grooves of the metafemora are covered by hydrofuge pubescence, which is an unusual condition among Neotropical acidocerines with mostly glabrous metafemora.

The smaller members of Ephydrolithus might resemble species of Crucisternum (see Girón and Short 2018), but the prosternal keel of Crucisternum easily separates them.

Description.

Small beetles, total body length 1.8-3.3 mm; body elongate oval, moderate to strongly convex in lateral view (e.g., Figs 5B , 6F ), yellowish brown to dark brown in color, sometimes paler along lateral margins of pronotum and elytra, legs (especially tarsi), mouthparts and antennae. Head. Frons and clypeus (e.g., Fig. 5H ) with moderately marked ground punctures, irregularly and rather densely distributed over the surface, with only few seta-bearing systematic punctures along lateral areas of frons and clypeus; surface between punctures smooth and shiny. Eyes oval in dorsal view, separated by nearly 5 × width of one eye; in lateral view, anterior margin slightly emarginate. Clypeus trapezoid, with medial surface moderately convex, and anterior corners forming widely rounded obtuse angles; anterior margin of clypeus widely roundly emarginate, 0.7 × width of posterior margin; membranous preclypeal area absent. Labrum 0.7 × as wide as anterior margin of clypeus, fully exposed, nearly 1/3 as long, and usually collinear to clypeus (e.g., Fig. 6D ); dorsal surface convex, with fine punctures; anterior margin roundly bent inwards, mesally emarginate and with tiny denticles along emargination; anterior corners fringed by setae. Temporae densely covered by very short and fine setae (hydrofuge pubescence). Mentum parallel sided, with surface mostly smooth and undulated, sometimes anteromesally depressed; anterior margin mesally depressed, usually depression marked by a u-shaped transverse carina. Submentum sunken and pubescent at base, glabrous, shiny, and ascending at apex; well-developed ocular ridge. Maxilla (see Fig. 6C ) with ventral surface of cardo and stipes smooth and shiny, at most with few scattered and shallow punctures; cardo positioned collinear to oblique to ventral surface of head; outer dorsal margin of palpifer with a row of stiff, decumbent, spiniform setae; limit between cardo and stipes parallel to posterior margin of mentum; maxillary palps curved inward, yellowish, nearly as long as antennae, short (e.g., nearly two thirds the width of the head) and stout (e.g., Fig. 6H ); palpomere 1 strongly widened near apex (with outer apical margin strongly convex); palpomere 2 gradually widening towards apex; palpomere 3 fusiform, bearing apical sensilla; all palpomeres similar in length. Mandibles with apex bifid (examined in E. ogmos ). Labial palps yellow, slightly shorter than mentum, dorsoventrally flattened; palpomere 2 with outer margin strongly convex apicad of midpoint, sometimes with one preapical seta on outer surface; palpomere 3 digitiform, with a long subapical seta on outer corner. Antennae (see Fig. 6C ) with nine antennomeres, usually yellow with darker club; antennomere 1 with surface evenly convex near base, reaching midpoint of ventral surface of eye (reaching cardo-stipes joint), 1.5-2.5 × longer than antennomere 2; antennomere 2 nearly as long as antennomeres 3-5 combined; antennomere 6 forming a well differentiated, asymmetric cupule; antennomeres 7-9 each wider than long, slightly flattened, forming a loosely articulated, pubescent club (antennomere 8 shortest, 9 longest); pubescence of antennomere 9 with few scattered longer setae on apical area. Thorax. Pronotum widest at base, narrowed anteriorly, surface evenly convex; ground punctation moderate, uniformly dense, with surface between punctures smooth and shiny; seta-bearing systematic punctures forming paired anterolateral semicircles, and paired short posterolateral transverse bands. Scutellar shield of moderate size, triangular, nearly as long as wide, with punctation as in pronotum. Prosternum flat (e.g., Figs 5C , 6C ), sometimes only slightly elevated along longitudinal midline (e.g., Fig. 5G ), nearly as long as half the length of a procoxa; anterior margin of prosternum straight to slightly convex; surface finely crenulate, with scattered fine setae, slightly impressed along procoxal area; intercoxal process projected from posterior margin of procoxal cavities, rectangularly shaped in outline, mesally longitudinally carinate. Mesoventrite (Fig. 7A, G ) not fused to mesepisterna, with anterior margin 0.2-0.4 × as wide as anterior margin of mesepisternum; anterior rib of mesoventrite with median, triangular, pale macula; posterior elevation of mesoventrite either with a sharp, low, transverse, curved ridge (Figs 5C , 7A ), or bearing a basally transverse, well-developed tooth that extends anteriorly as a longitudinal carina (Figs 6C , 7G ); surface of mesoventrite with posterolateral smooth and glabrous areas; mesepisternum obliquely widely concave; mesepimeron trapezoid, with pubescent surface. Mesofurca (examined in E. hamadae ) with short arms, 0.9 × length of mesocoxae; apical half of arms free, somewhat triangular at apex. Metaventrite posteromesally elevated, with elevation somewhat narrow anteriorly, widening posteriorly; surface of metaventrite densely pubescent, except for a median to posteromedian, large teardrop-shaped glabrous patch; anteromedian area of metaventrite with a deep and narrow transverse depression before anterior intercoxal process. Metepisterna nearly 4 × longer than wide, slightly narrowing at posterior end. Metepimeron triangular and posteriorly slightly projected. Metafurca (examined in E. hamadae , Fig. 7B ) 1.3 × wider than long, with furcal arms 0.8 × the length of stalk; stalk triangular (wider near the crux, gradually narrowing ventrally), with paired longitudinal keels extending along basal third of posterior face, fusing together towards crux, with a well-developed median keel on anterior face extending to anterior margin of dorsal sheets; outer margins of stalk diverging from basal third towards crux; furcal arms somewhat trapezoid, with apex (hemiductus) roundly explanate, with apex pointing laterally; anterior tendons inserted at basal third of dorsal edge of furcal arms; well-developed dorsal sheaths, wider than widest point of lateral sheaths. Elytra. Surface even (without elevations or depressions), without sutural striae (in E. ogmos elytral striae well-marked, more strongly so along stria 1); ground punctures sharply marked, uniformly and rather densely distributed; seta-bearing systematic punctures rather enlarged and deep, forming five longitudinal rows along each elytron, fifth row very close to outer margin of elytron; serial punctures usually absent (present but reduced in E. ogmos ); elytral margins slightly flared. Epipleura well developed, surface rather oblique, with fine setae, anteriorly wide, gradually narrowing posteriorly, extending up to line of posterior margin of metaventrite; inner margin of epipleura slightly concave at articulation of anterior outer corner of metepisternum; well-developed pseudepipleura, rather obliquely positioned, anteriorly nearly as wide as anterior portion of epipleura, narrowing towards line of posterior margin of metaventrite, extending as narrow band along remainder outer margin of elytron. Hind wings well developed (examined in E. hamadae and E. teli ). Legs. Pro- and mesofemora covered with hydrofuge pubescence along at least basal half; metafemora with hydrofuge pubescence as a narrow stripe along basal 2/3 of anterodorsal margin, remainder anterior surface usually smooth and shiny, with only few scattered setae; all femora antero-posteriorly flattened, with sharp tibial grooves; sometimes tibial grooves with hydrofuge pubescence (in E. hamadae and E. teli ). Tibiae slender, weakly flattened, with well-developed spines; protibiae with a median longitudinal row of long setae along anterior surface; apical spurs of protibiae rather large and slender. All tarsi with five tarsomeres, bearing long apical hair-like setae on dorsal face, and two lateral rows of hair-like spines on ventral face of tarsomeres 2-4; pro- and mesotarsomeres 1-4 similar in size and shape; pro- and mesotarsomere 5 similar in size to pro- and mesotarsomeres 1-4 combined; metatarsomere 2 nearly as long as tarsomeres 3-4 combined; metatarsomere 5 similar in size to metatarsomere 2, without spines on ventral face; claws rather large, curved; well-developed empodium, bearing a pair of long, curved apical setae. Abdomen. Abdomen with five ventrites, very weakly convex medially; all ventrites with uniform, dense, fine pubescence; posterior margin of fifth ventrite truncate, set with a row of thick, flat spine-like setae (Fig. 7C ). Aedeagus (Fig. 7 D–F, H, I ) with outer margins convex, straight or sinuate, with basal piece between 0.45 and 0.9 X the length of parameres; median lobe somewhat triangular in shape, with well-developed lateral basal apodemes; widest point of median lobe wider than widest point of each paramere; apex of median lobe widely to narrowly acute, sometimes “pinched” (e.g. E. hamadae , Fig. 7D ); parameres nearly as long as median lobe, with greatest width near base, bearing apical setae; well-developed gonopore, preapically situated.

Larvae.

The immature stages are unknown.

Etymology.

Named by the combination of the Greek words ephydros meaning wet, and lithus meaning rock, in reference to the seepage habitat in which the genus has been collected. To be treated as neuter.

Distribution.

The genus is currently only known from the northeastern highlands of Brazil ( Bahía, Minas Gerais) on the Brazilian Shield (Fig. 8 ).

Remarks.

Species of Ephydrolithus have been collected in an altitudinal range between 568 and 1705 m. All known species are exclusively associated with rock seepages (see Fig. 9 ).

Figures

Figure 5. Habitus of Ephydrolithus spp.: A-D Ephydrolithus hamadae: A dorsal view B lateral view C ventral view D head, dorsal view. E-H Ephydrolithus teli: E dorsal view F lateral view G ventral view H head, dorsal view. Scale bars: 1 mm.

Figure 6. Habitus of Ephydrolithus spp.: A-D Ephydrolithus ogmos: A dorsal view B lateral view C ventral view D head, dorsal view. E-H Ephydrolithus minor: E dorsal view F lateral view G ventral view H head, dorsal view. Scale bars: 1 mm.

Figure 7. Thorax, abdomen and genitalia of Ephydrolithus spp.: A-D Ephydrolithus hamadae: A ventral view of mesoventrite (white arrow pointing transverse ridge) B posterior view of metafurca C fifth abdominal ventrite D aedeagus E aedeagus of Ephydrolithus teli. F, G Ephydrolithus spiculatus: F aedeagus G oblique view of mesoventrite (black arrow pointing well-developed tooth) H aedeagus of Ephydrolithus ogmos I aedeagus of Ephydrolithus minor. Scale bars: 0.25 mm.

Figure 8. Distribution of Ephydrolithus spp.

Figure 9. Habitat of Ephydrolithus spp. A, B habitat and type locality for E. minor and E. ogmos, Brazil, Pico do Barbado, collecting event BR 18 - 0226 - 01 C C habitat and type locality for E. hamadae and E. spiculatus, Brazil, Cachoeira da Palmeira, collecting event BR 18 - 0302 - 04 A D habitat and type locality for E. teli, Brazil, Pico do Barbado, collecting event BR 18 - 0226 - 01 B.