Meru, Spangler & Steiner, 2005

Spangler, Paul J. & Steiner, Warren E., 2005, A new aquatic beetle family, Meruidae, from Venezuela (Coleoptera: Adephaga), Systematic Entomology 30 (3), pp. 339-357 : 340-347

Meru gen.n.

Type species. Meru phyllisae , sp.n.

Description. Size very small, length 0.85–0.9 mm; width 0.38–0.41 mm. Body form generally ovate, convex dorsally, less so ventrally ( Fig. 1 ), widest at basal quarter of elytra; prothorax broadly attached to mesothorax and elytral base ( Fig. 2 A–I). Colour generally dark brown to yellowish brown. Most surfaces of body bearing flat, wrinkled ‘setae’ (possibly membranous papillae; see comments below) arising from the anterior side of large, shallow punctures.

Head ( Figs 2A, B, D, E , 3A, B ) prognathous, slightly longer than wide, with retracted neck region; eyes lateral, broadly elliptic, prominent; ommatidia numbering five by nine across axes of eye. Frons smooth, slightly convex, with reticulate microsculpture; laterally and basally with scattered shallow punctures and fine setae; frontoclypeal suture obscure; labroclypeal suture nearly straight. Labrum trapezoidal, with scalelike microsculpture; front edge with a shallow median notch covered by opposing, overlapping, spatulate setae ( Fig. 3E ) and with three tapered setae originating from small pits lateral to base of spatulate seta; a pair of small, flat, toothlike setae imbedded in the anterior margin of the notch. Antenna ( Fig. 4 A–F1) longer than head, filiform, glabrous, eleven-segmented; scapus very short and nearly hidden; pedicellus almost globular, urn-shaped, bearing a few slender setae; antennomere III as long as pedicellus but more narrow, nearly twice as long as wide, subcylindrical, thickest towards apex; antennomeres IV–X of similar form, but V, VII and IX longer and thicker than the adjacent ones; antennomeres VII and IX bearing a platelike sensorial patch ventrally; antennomere XI longer than the preceding two combined, thickest at middle and obliquely tapering to a narrow apex, with two platelike sensorial patches near apex on ventral side. Mandibles ( Fig. 7A ) nearly twice as long as wide, with a single, blunt, falcate, apical incisor and median terebral tooth; brushes of trichiae, molar teeth, and retinaculum absent. Left mandible slightly longer than right, terebral tooth broadly angular; inferior terebral ridge with one or two minute teeth. Right mandible with terebral tooth truncate and closer to apex than that of left mandible; basal face with several small wrinkles. Maxilla ( Fig. 7B ) with cardo small, wedge-shaped; stipes and lacinia fused; lacinia stout, elongate, glabrous, with a curved, robust apical spine and seven setae on inner side; galea simple, two-segmented, shorter than lacinia, with apical segment elongate, cylindrical, smoothly rounded at apex; palpus four-segmented; apical segment slightly longer than combined length of segments 1–3, with sensory structures on the distal part ( Fig. 3 F–H). Submentum broad, with distinct tentorial pit at basolateral corner ( Figs 2E , 3C ); mentum flat, smooth, slightly more than half as wide as head, with two long setae on each side at approximately middle; prementum recessed, inserted between anterolateral rounded lobes of mentum; base of palpifer with a single small seta; ligula moderately extended and rounded apicomedially, with twelve to fourteen apical setae ( Fig. 3C, D ); labial palpus three-segmented; apical segment swollen and slightly longer than combined length of segments 1 and 2, with apical sensory structures ( Fig. 3C, F, I ) similar to those of maxillary palpus.

Prothorax ( Figs 2D, E, I , 8A ) about four-fifths as wide as elytra; pronotum widest at base, slightly wider than long, lateral margin sinuate, not beaded; anterior margin straight, anterior corners narrowly rounded; posterior corners angled; posterior margin nearly straight between corner and middle, tightly fitted against base of elytron and forming an angle of about 125 with other side at middle; disk evenly convex, surface with four shallow depressions on each side; surface coarsely, densely punctate; each puncture with a long, robust, flattened and wrinkled seta, pleated at base, arising from anterior edge of puncture and recumbent across it; length of seta about twice the diameter of a puncture; scattered, hairlike setae also present, arising from smooth areas between the large punctures. Thoracic sternites with a similar combination of setae and punctures, but larger and more sparsely placed laterally. Prosternum ( Figs 2E , 8A ) with notopleural and pleurosternal sutures visible; propleuron large, extending behind coxa; procoxal cavity closed internally. Cervical sclerite absent. Anterior margin of prosternum evenly arcuate with a fine fringe of microsetae along edge and on each side with one large, anteriorly directed, club-shaped seta, with apex flattened and toothed, brushlike ( Fig. 2E ). Prosternal process very narrow between procoxae but wider and truncate behind them ( Fig. 8A ). Mesosternite, metasternite and lateral part of metacoxae fused, with sutures not discernible laterally ( Fig. 8B ); mesosternite with pentagonal depression partly covered by (articulated with) prosternal process. Transverse ridge of metaventrite absent. Metacoxal plates small, not covering base of trochanter, with lateral margins indistinct anteriorly; median lamina of metacoxae not distinctly separated from lateral part; posterior margin straight, with a small median emargination and deep incisions for trochantinal articulations ( Figs 2C, F , 8B ). Metendosternal process slender, median ridge (metacoxal septum) attached to the metasternite for two-thirds of its length, ending with a slenderarmed, Y-shaped metafurca anteriorly ( Figs 9 , 10A, B ).

Scutellum not visible. Elytron convex, twice as wide as long, dorsally with setae and punctures like those on pronotum ( Fig. 5A, B ) in addition to rows of large, deep, strial punctures that do not bear setae; sutural stria absent and sutural edge not beaded; lateral margin arcuate in lateral view ( Fig. 5A ); epipleuron indistinct; inner surface smooth, laterally with a large, locking pit at about midlength and a round patch of granular surface (presumably for wing folding) anterior to it ( Fig. 5C, D ). Hind wings dimorphic ( Fig. 11A, B ), either fully developed with venation moderately developed and distal half folded ( Figs 11B , 12 ), or brachypterous, as long as elytron, with venation very reduced and distal half appearing shrunken ( Fig. 11A ); margins with a fringe of long setae; subcubital binding patch absent; oblongum cell not discernible. Procoxa and mesocoxa globular; trochanters smooth, unmodified. Metatrochanter large, about twice the size of pro- and mesotrochanter, globular, swollen posteriorly; junction with metafemur oblique and sinuate. Femora smooth, club-shaped, widest at about apical third, with scattered sparse hairlike setae, some brush-tipped, and a row of five to seven thick, branched setae on dorsal surface. Metafemur very slender basally, attached dorsolaterally to trochanter; distal two-thirds swollen. Tibiae simple, straight, gradually thickening from base to near apex, with sparse hairlike setae, irregularly distributed, becoming more stout towards apex of tibia; each tibia bearing a pair of toothed apical spurs, both trident on pro- and mesotibia, one trident and one laterally pectinate on metatibia ( Fig. 6 A–F). Tarsal formula 5-5-5; last tarsomeres longer than combined lengths of the preceding two; tarsomeres 1 and 2 each with four stout, ventral setae, 3 and 4 with two setae, and 5 with one seta; hind tarsus with basal tarsomere longest; length equals combined length of tarsomeres 2–4. Tarsal claws large, pectinate, with four to five teeth ( Fig. 6 G–I). Empodium small, smooth, padlike.

Abdomen with six visible sternites (morphological sterna II–VII); visible sternites 1, 2 and 3 completely fused, with sutures indistinct (positions marked by row of setae); first visible sternite deeply and broadly divided medially for reception of metacoxal processes ( Fig. 13 ), internally with a heavily sclerotized, transverse septum along posterior margin; posterior margins of sterna 1–5 bearing a comblike row of robust, flattened and grooved setae and forming a fringe along with fewer hairlike setae ( Figs 2F , 5E, F , 8B ); sternites 1 and 2 with punctures bearing robust wrinkled setae scattered over surface; the flat pleated setae on sternites 3–5

Wrinkled flat setae on the body. These appear to be membranous papillae, very different from the normal, fine setae among them. It is possible that these structures may have a respiratory function, but determining their connection to the tracheal system was beyond the scope of this study. On dry beetles examined under the scanning electron microscope, broken examples of the papillae have been seen and they are hollow, but details of the basal attachment have not been clearly viewed; no opening to the cuticle was observed.

Etymology. ‘Meru’ means ‘waterfall’ in the language of the Pemon people of the tepui region of Venezuela.

Figures

Fig. 1. Meru phyllisae, scanning electron micrograph, lateral habitus.

Fig. 2. Meru phyllisae. Scanning electron micrographs. A, Habitus, dorsal view; B, habitus, ventral view; C, thoracic sterna; D, head, pronotum and bases of elytra; E, head and prosternal area; F, metasternum and abdomen; G, right elytron; H, pronotal and elytral bases; I, pronotum, lateral view.

Fig. 3. Meru phyllisae. A, Head, lateral view; B, head, anterior view; C, mouthparts, ventral view; D, labial palpal bases; E, head, anterior view, detail of mouth; F, right maxillary and labial palpi, ventral view; G, right maxillary palpus, apex; H, left maxillary palpus, apex; I, right labial palpus, apex.

Fig. 4. Meru phyllisae, antennae. A, Left, dorsal view; B, right, segments 1–7, ventral view; C, right, segments 7–11, ventral view, showing sensorial patches on segments 7, 9 and 11; D, right, segments 6–8, ventral view, showing sensorial patch on segment 7; E, left, lateral view, apical (eleventh) segment with sensorial patches; F, right, ventral view, apical (eleventh) segment with sensorial patches.

Fig. 7. Meru phyllisae. A, Mandibles, dorsal view; B, maxilla, left, ventral view.

Fig. 8. Meru phyllisae, sterna. A, Outline of prothorax; B, hind body.

Fig. 9. Meru phyllisae, metendosternite, dorsal view.

Fig. 10. Meru phyllisae, metendosternite, scanning electron micrographs. A, Oblique dorsolateral view; B, dorsolateral view.

Fig. 5. Meru phyllisae. A, Left elytron, lateral view; B, left elytron, detail of margin; C, left elytron, inner surface; D, left elytron, wing-folding patch on inner surface; E, abdominal sternites, detail of posterior margins of 1–3; F, abdominal sternite 3, detail of posterior margin.

Fig. 11. Meru phyllisae, hind wing. A, Brachypterous condition; B, macropterous condition.

Fig. 12. Meru phyllisae, hind wing, macropterous condition, in folded position.

Fig. 6. Meru phyllisae. A, Front and mid legs, left, anterior view; B, front and mid legs, right, posterior view; C, D, mesotibia, right, apex; E, hind tarsus, left, ventral view; F, hind tarsus, left, posterior view; G, claws, right mesotarsal, lateral view; H, claws, left metatarsal, oblique view; I, claws, right metatarsal, ventral view.

Fig. 13. Meru phyllisae, visible abdominal sterna.