Horologion hubbardi Harden & Davidson, 2024

Harden, Curt W., Davidson, Robert L., Malabad, Thomas E., Caterino, Michael S. & Maddison, David R., 2024, Phylogenetic systematics of the enigmatic genus Horologion Valentine, 1932 (Coleoptera, Carabidae, Trechinae, Horologionini), with description of a new species from Bath County, Virginia, Subterranean Biology 48, pp. 1-49 : 1

Horologion hubbardi Harden & Davidson sp. nov.

Figs 2 , 3D , 8 , 9D-H , 10 , 11B-E , 12

Type material.

Holotype male (Suppl. material 3: fig. S1B) (CMNH), point mounted, abdominal ventrites and right protibia and protarsus glued to point, genitalia in plastic glycerin microvial pinned beneath specimen labels. Original labels: "USA: VIRGINIA, Bath Co. Williams Cave. 29.March.2023. T. Malabad, C. Harden, K. Kosič Ficco. Found floating on pool surface." "Harden DNA Voucher CWH-484 H. m Ext. 12/April/2023 [green-bordered cardstock]" "[QR code] CMNH-IZ 769,132" "HOLOTYPE Horologion hubbardi ♂ Harden & Davidson [computer printed on red cardstock]". COI GenBank accession: OR500887.

Paratypes (n = 4): One female (VMNH), point mounted, abdominal ventrites and genitalia in glass glycerin vial pinned beneath specimen, labeled "USA: VIRGINIA, Bath Co. Williams Cave. 2.August.2022. T. Malabad, D. Hubbard, C. Harden. Active on ground near drip pool." "Harden DNA Voucher CWH-452 H. Williams F Ext. 7/August/2022" [green-bordered cardstock]. GenBank: OR505843, OR505933, OR500886, OR503053, OR503061, OR503098, OR503071, OR503063, OR503052.

One female (CMNH), point mounted, not dissected, labeled "VIRGINIA: Bath County, Williams’ Cave, Sep 8 1991" "D.A. Hubbard" "THOMAS C. BARR COLLECTION 2011 Acc. No. 38.014" "VANHP #: Hubbard VA: Co: Bath Loc: Williams Cave Date: 8 Sept 91." "[QR code] CMNH-IZ 769,133".

Two males (VMNH), dry mounted with genitalia in glycerin, missing most of antennae and legs, labeled "USA: VIRGINIA, Bath Co. Williams Cave. 28.March.2023. T Malabad, K. Kosič Ficco, CW Harden. Found dead.".

Other material.

Fragments of three specimens, one male, one female, and one unknown sex, in alcohol vials (VMNH): Found dead in or near small pools, Williams Cave, 29 March 2023 .

Diagnosis.

From Horologion speokoites , this species differs in the following external characters: the elytral humeri have longer carinal shelves that terminate in a sharp, curved spine (Fig. 10D ); the elytra are flatter (Fig. 11 ); and the two basal protarsomeres of males are asymmetrically dilated and spinose on their inner margin (Fig. 8A ). The male genitalia (Fig. 9D-G ) also differ from those of H. speokoites (Fig. 9A-C ): the parameres are smaller and each bear three apical setae, the median lobe is straighter ventrally, not twisted from plane of basal lobes, with a smaller and more symmetrical apex, and the flagellum of the internal sac is slightly longer and without a distinct sinuation.

Description.

Habitus: Average sized for Trechinae (ABL = 3.16-3.20 mm), pubescent, without trace of eyes. Variable in color, dark castaneous in the 1991 specimen (Suppl. material 3: fig. S1A) (possibly stained due to unusual ethanol preservation) and lighter in fresher specimens (Fig. 2 , Suppl. material 3: fig. S1B); integument strongly sclerotized; proportions delicate, with pedunculate pro-mesothoracic junction; elytra vase shaped, with prominent humeral carinae ending in curved spines. Appendages relatively short; body flattened dorsoventrally.

Head: Relatively large (HW/PW = 0.84-0.86); temples rounded; eyes entirely absent. Dorsal surface evenly covered with short, light-colored setae set in coarse circular pits. Microsculpture consisting of weakly impressed, irregular scalelike sculpticells, except a subtriangular patch on vertex where the sculpticels are coarse and conspicuous. Occipital region (concealed by pronotum) smooth, demarcated from rough vertex by a curved marginal line. Vertex with anterior supraorbital seta present on each side (Fig. 12A ); posteriorly with 3 to 5 pairs of moderately long inward-facing setae in a transverse row, none of which arise from a pore of comparable size to the anterior supraorbital setae. Frontal grooves weakly defined, shallow and short, ending at level of anterior supraorbital setae. Frontoclypeal suture weakly impressed, without carinae or horn like projection. Clypeus transverse, subrectangular, with four large fixed setae, outer pair erect and longer than inner pair; inner pair appressed, arising from smaller pores than outer pair (Suppl. material 3: fig. S3C); in addition to scattered background setae, two thin setae the same length as inner pair are present near anterior angles (Fig. 12A ). Labrum transverse, similar in size and shape to clypeus; anterior margin slightly crenulate, protruding slightly forward at each setiferous pore insertion; six fixed apical setae present, decreasing in length from outer to inner pairs. Ventral surface of head with a long suborbital seta on each side, set just anterior to the arcuate gular impression; tentorial pits present at anterior end of gular sutures, with small slit like openings; ventral surfaces pubescent anterior to gular impression, except strip between gular sutures, which is also strongly microsculptured with coarse, small sculpticels; microsculpture also strong within gular impression, and along margins of maxillary grooves, weak elsewhere.

Antennae: Length approximately half of body length (AntL/ABL = 0.51-0.53). All antennomeres pubescent, filiform; antennomeres I-X with a subapical ring of long setae, antennomere XI with a ring of long setae just beyond middle, and a crown of long setae at apex. Several small, circular pores scattered in apical half of antennomere XI, concentrated near apex. Antennomere I shorter and thicker than antennomeres II-X. Four apical antennomeres gradually increasing in width; antennomere XI largest, slightly longer than antennomere II and clearly longer than all other antennomeres; gradually tapered apically. Antennae similar in both sexes.

Mouthparts: Mandibles with scrobal seta present; narrow and elongate, both similar in size and shape but differing in dentation: right mandible with prominent anterior retinacular tooth, terebral tooth, posterior retinacular tooth and molar tooth; left mandible without anterior retinacular tooth, with small terebral, posterior retinacular and molar teeth (Suppl. material 3: fig. S3A, B). Mentum and submentum separated by suture; submentum generally setose, with two pairs of long fixed setae, inner pair very long (the longest ventral setae of head); mentum transverse, surface glabrous except for two pairs of fixed setae, inner pair situated well behind mentum tooth; mentum shallowly biconcave, each concavity with a small irregular pit with numerous small pores; mentum tooth carinate, entire, long and acute (Fig. 12C ). Labial palps glabrous except for penultimate palpomere, which has four long setae; apical palpomere long, much narrower than penultimate. Ligula carinate medially, with distinct paraglossae; anterior margin between paraglossae with six setae, an outer pair of very short setae, a submedial pair of moderately long fixed setae, and a medial pair of long fixed setae that are conjoined, arising from adjacent pores, appearing as one long seta except in SEM images; short outer pair not visible under a stereoscope at 100 ×, but visible in SEM images (Suppl. material 3: fig. S4A). Maxillary palps glabrous except second palpomere, which bears two setae on outer surface near apex; second and third palpomeres somewhat globular; apical palpomere narrow and elongate, but not truly subulate (basal width subequal to apical width of penultimate palpomere) (Fig. 12A ).

Prothorax: Pronotum small, narrower than elytra (PW/EW = 0.67) and less than one fourth body length (PL/ABL = 0.23); greatly narrowed posteriorly (PbW/PW = 0.39). Surface densely covered in light-colored setae, each set in a circular pore; setae whorled along midline: facing posteriorly in posterior half, medially in middle, and anteriorly in anterior half. Median longitudinal sulcus well impressed, but not reaching anterior or posterior margins. Lateral marginal bead lacking except for a short distance near lateral setae; otherwise, dorsal surface and hypomeron continuous. Posterior angles obsolete, without lateral setae; posterior impressions lacking. Posterior margin without bead, dorsal surface curved beneath itself, forming a smooth shelf that overhangs the mesothoracic pedicel. Prosternum (Fig. 12C ) shorter than pronotum, ending anteriorly and posteriorly well before pronotal extent; setose medially; propleuron glabrous. Pleurosternal suture meeting hypomeron anteriorly behind anterior angles of prosternum, which are produced forward, overlapping hypomeron. Procoxal cavities bordered by raised margin anteriorly; closed posteriorly by propleuron narrowly joining intercoxal process (Fig. 12B ). Intercoxal process elongate, acuminate posteriorly. Procoxae coarsely microsculptured, glabrous; protrochanters small, setose, with single large fixed seta near apex; femora and tibiae slender and setose, tibiae strigose on outer margin; outer margin declivitous in dorsal view, but without distinct notch (Fig. 8A ). Inner margin of tibiae with large antenna cleaner of typical "grade B" ( Hlavac 1971), i.e. with a sinuate longitudinal band of tightly packed setae within the channel; arrangement of terminal spurs anisochaetus, i.e. situated at opposite ends of the setal band; anterior spur stouter than posterior; one large clip seta present. Tarsi densely setose and very short; protarsomeres 2-IV distinctly transverse, wider than long, each with a pair of long setae ventrally, ventral setae of protarsomere III longest and conspicuous; protarsomere IV with a thick medial ribbonlike seta that surpasses apex of tarsus; tarsal claws simple and evenly curved, without basal tooths or serrations, relatively elongate, longer than protarsomere V; males (Fig. 8A, C-D ) with protarsomeres I and II asymmetrically expanded and dentate on inner margin, with a single row of at least seven adhesive setae on venter of inner dentate expansions; females with protarsomeres I and II symmetrical, not dentate and without ventral adhesive vestiture, protarsomere I slightly longer than wide, protarsomere II transverse, subequal to protarsomere III.

Pterothorax: Elytra moderately long, length slightly more than half of ABL; scutellum very narrow and elongate (Fig. 10D ). Elytra fused along suture for most of their length, narrowly separated in apical fourth. Dorsal surface evenly setose, with short light-colored setae each set in a deep circular pit; microsculpture weakly impressed, sculpticels irregularly shaped, scale like and longitudinally stretched. Humeri each bearing an angulate shelf, flanked proximally by a strong carina and ending in a prominent curved spine; lateral bead of elytra moderately crenulate beyond humeral spine for a short distance and smooth beyond that (Fig. 10D ). Each elytron with a parascutellar seta, four subhumeral lateral setae, two submedial lateral setae, three apical setae (two lateral and one discal, in the position of the "subapical seta" of Schmidt et al. (2021), umbilicate pore “8” of anilline taxonomists ( Giachino and Vailati 2011; Sokolov 2013)), and one discal seta in third interval at about the level of fifth lateral seta (Fig. 11B, D ); discal seta indistinguishable from background pubescence in low-magnification dorsal view but distinctly visible in oblique or lateral views (Fig. 11B ) or at higher magnification (Fig. 11D, E ); second subhumeral, second submedial, and posterior-most apical seta greatly elongate and filamentous. Ventral surface of elytra each with a well-developed lateral plica near apex, its surface strongly microsculptured with scale-like sculpticells (Fig. 11E ). Mesoventrite (Fig. 10B ) with coarse isodiametric microsculpture; narrow, much longer than metaventrite; extended anteriorly as a parallel-sided pedicel that extends beyond posterior extent of pronotum; surface of pedicel strongly rugose, with numerous transverse furrows; posterior half of mesoventrite with a medial longitudinal depression flanked by low, parallel carinae that coalesce anteriorly, each carina bearing a pair of long setae; medial depression extending posteriorly onto intercoxal process. Mesanepisternum and mesoventrite apparently fused, without discernible suture; mesocoxae conjunct, i.e., entirely enclosed by mesoventrite and metaventrite, mesepimeron not meeting mesocoxae (Fig. 10A ). Mesocoxae with coarse scale-like microsculpture and sparse setae, each with a well-developed knob on inner margin; mesotrochanters densely setose but without apparent macrosetae; mesofemora and mesotibiae slender, setose except for glabrous area on posterior face of femora; inner face of mesotibiae strigose; apical half of mesotibiae with dense brush of coarse setae; apex of mesotibiae with adjacent pair of short spurs on posterior margin, barely extending past length of first mesotarsomere; mesotarsi of both sexes similar in form to female protarsi. Metaventrite (Fig. 10C ) short, setose and coarsely microsculptured, with shallow medial depression; intercoxal process cleft posteriorly; metanepisternum and metaventrite separated by suture; metepimeron visible (Fig. 10A ), overlapping first abdominal ventrite. Metacoxae setose, without apparent macrosetae; well separated, distance between them approximately equal to width of one mesocoxa; metatrochanters small, approximately equal in length to metacoxae, gradually narrowed apically, not strongly pointed; metafemora and metatibiae similar to those of mesothoracic legs, except metatibiae lack dense brush of setae; metatarsi more elongate than tarsi of other legs, metatarsomeres slightly longer than wide, gradually increasing in length from I to IV, V slightly longer than combined length of III and IV; medial ribbonlike setae on apex of metatarsomere IV narrower than on pro- and mesotarsi.

Male genitalia: Relatively small (Length of ring sclerite / ABL = 0.16); ring sclerite similar to that of H. speokoites ( Valentine 1932, fig. 13): yoke shaped, posterior margin produced as an obtuse angulation, narrowed anteriorly where sides join to form a short, flattened extension that is curved ventrally at its slightly asymmetrical apex. Median lobe of aedeagus (Fig. 9D ) broad and lightly sclerotized, with entire dorsal margin and most of ventral face membranous; basal lobes and sides of ventral margin sclerotized and giving the organ a trough-like shape; ventral margin in lateral aspect slightly curved in proximal half, with membranous portion sagging below; apex small, extended a short distance past membranous dorsal margin and appearing evenly rounded and symmetrical in dorsal aspect; median lobe not twisted from plane of basal lobes (Fig. 9F ). Left paramere (Fig. 9E ) relatively large and subtriangular, with numerous pores on dorsoapical margin and three apical setae. Right paramere (Fig. 9G ) slightly smaller than left paramere, and more styliform, with numerous pores on dorsoapical margin and three apical setae. Internal sac of median lobe with well sclerotized flagellum surrounding a small spine and a ventral field of small sclerotized scales; flagellum rotated dorsally, so that in lateral aspect it appears as a complex folded structure (Fig. 9D ); in dorsal aspect strongly curved (Fig. 9F ), swollen and spiraled proximally at junction with sperm duct, abruptly narrowed beyond this region, very gradually tapering toward apex.

Female genitalia: (Fig. 9H ) Gonocoxite 2 narrow, moderately long and weakly curved, bearing numerous pores and a single short preapical seta on inner margin. Tergite X well-sclerotized and forming a subtriangular bridge behind gonocoxites. Spermatheca and spermathecal gland present; spermathecal duct relatively wide and moderately long, with an abrupt U-shaped bend proximally; spermatheca small and pouchlike; spermathecal gland long and narrow, arising from base of spermatheca near junction with duct.

Distribution.

Known only from Williams Cave, in Bath County, Virginia. In the database of the Virginia Speleological Survey (VSS, https://www.virginiacaves.org/), this cave is number 2779.

Sympatry.

Williams Cave is also home to the eyeless trechine Pseudanophthalmus intersectus Barr, which also occurs in two other nearby caves in Bath County (Virginia DCR-DNH data). An individual of this species was found in the same microhabitat as the female paratype of H. hubbardi , and members of the two species presumably occur in syntopy. The only other carabid beetle known from Williams Cave is the surface tachyine Paratachys scitulus (LeConte), a common and widespread species in eastern North America; one specimen was found in organic debris just inside the entrance in August 2022.

Natural history.

Williams Cave is a large cave, with a surveyed length of 5.39 km (VSS data). The cave is shallow in relation to the overlying surface topology and is damp in places, with numerous ceiling drips and small pools. Most water in the cave is recharged through these ceiling drips. All specimens of H. hubbardi were found in or near small pools of water. Specimens were collected in March, August and September. Specimens from 2022 and 2023 were collected in somewhat distant sections of the cave, but COI sequences of the two are identical, suggesting they are not isolated. Immature life stages are unknown.

Species status justification.

The differences in male protarsi (first and second protarsomeres asymmetrically expanded and dentate in H. hubbardi , only first protarsomere weakly dentate in H. speokoites ), the form of the elytra (flattened, with prominent curved spines on the humeri in H. hubbardi , convex and with a small humeral carinal shelf without spines in H. speokoites ), and the male genitalia, particularly the parameres (tapered and with 3 apical setae in H. hubbardi , broad and blunt with 6 apical setae in H. speokoites ) are great enough to warrant recognition of the two as distinct taxa that are reproductively isolated. The two species are also geographically isolated, occurring 70 air km distant and on the opposite side of several large ridges of noncarbonate rock with numerous peaks above 1200 m, indicating complete isolation of these blind subterranean beetles (Fig. 13 ).

Derivation of name.

This species is named in honor of its discoverer, David A. Hubbard, Jr., in recognition of his important contributions to cave biodiversity and conservation. In addition to many significant collections of cave carabids in Virginia, notable discoveries by Hubbard include the single known specimen of the Chinese stygobiontic dytiscid genus Sinodytes ( Spangler 1996) and a highly modified species of the pselaphine rove beetle genus Mipseltyrus that remains undescribed (C. Harden, personal observation).

Suggested vernacular name.

“Hubbard’s Hourglass Beetle".

Figures

Figure 2. Horologion hubbardi female paratype, voucher CWH- 452 (VMNH), dorsal habitus. Abdomen removed for DNA extraction. Scale bar: 1 mm.

Figure 3. Habitat of species of Horologion A surface habitat at Williams Cave, Bath Co., VA B C. Harden (yellow helmet) and T. Malabad (red helmet) in microhabitat of H. hubbardi voucher CWH- 452 in Williams Cave C C. Harden examining live H. hubbardi holotype in Williams Cave D live holotype male of H. hubbardi on surface of drip pool in Williams Cave E surface habitat at Arbuckle Cave, Greenbrier Co., WV F T. Malabad examining flowstone in Arbuckle Cave. Photo credit: C. Harden (A, E), K. Kosic Ficco (B-D), M. Miller (F).

Figure 8. Protarsi of Horologion A H. hubbardi male holotype, dorsal aspect B H. hubbardi female paratype, dorsal aspect C H. speokoites male holotype, dorsal aspect D H. hubbardi male holotype, ventral aspect E H. hubbardi male holotype, dorsal aspect. Scale bars: 0.10 mm.

Figure 9. Genitalia of Horologion species A H. speokoites median lobe, left lateral aspect B H. speokoites left paramere, left lateral aspect C H. speokoites median lobe, dorsal aspect D H. hubbardi median lobe, left lateral aspect E H. hubbardi left paramere, left lateral aspect F H. hubbardi median lobe, dorsal aspect G H. hubbardi right paramere, right lateral aspect H H. hubbardi female genitalia, ventral aspect A-C after Valentine (1932). Scale bar: 0.1 mm.

Figure 10. Scanning electron microscope images of Horologion hubbardi female paratype, voucher CWH- 452 (VMNH) A detail of right side of pterothorax, ventral aspect B mesoventrite, ventral aspect C metaventrite, ventral aspect, abdomen removed D detail of humeral region of right elytron, dorsal aspect.

Figure 11. Elytral characters of Horologion species A H. speokoites holotype, elytra, oblique left lateral aspect B H. hubbardi paratype (CMNH), ditto C H. hubbardi paratype (VMNH), SEM detail of apex of left elytron, ventral aspect D H. hubbardi paratype (VMNH), SEM photo of right elytron, dorsal aspect E H. hubbardi paratype (VMNH), SEM detail of right elytron (area indicated by black box in D). Black arrows: discal setae, white arrows: plica.

Figure 12. Scanning electron micrographs of the forebody of Horologion hubbardi A head of voucher CWH- 452, dorsal aspect, clypeal setae indicated by white arrows B prosternum of non-type specimen, posterior aspect (head, pronotum and most of leg segments removed) C forebody of voucher CWH- 452, ventral aspect.

Figure 13. Distribution map of species of Horologion. Black triangle: Horologion hubbardi, black circle: Horologion speokoites. Grey shaded areas represent exposed karst (Weary and Doctor 2014).