Elachistelmis tetramera, Maier, Crystal A., 2012

Maier, Crystal A., 2012, Elachistelmis gen. n. (Coleoptera: Elmidae: Elminae) from Suriname, with description of two new species, Zootaxa 3500, pp. 61-69 : 63-66

Elachistelmis tetramera sp. n.

( Figs. 1–6 , 9–11 , 15–21 )

Type material. Holotype male: “ SURINAME: Sipaliwini District/ 2°10.973’N, 56°47.235’W, 210m / Camp 2, on Sipaliwini River/ leg. A.E.Z. Short; UV-light/ 27.viii–1.ix.2010; SR10–0827–LT2” Holotype deposited in the NZCS.

Paratypes: 45 specimens, same data as holotype. Paratypes will be deposited in: 5 in NZCS, 5 in NMPC, 5 in BMNH, 10 in NMW, 10 in SEMC, 5 in NHNM, and 5 in USNM.

Diagnosis. This species can be distinguished from all other described species of Elminae by the combination of its small size (ca. 1.0 mm) and tetramerous tarsi ( Figs. 15 & 17 ). This is possibly the smallest described riffle beetle in Elminae and the only species of elmid that does not have a 5–5–5 tarsal formula. Other characters that are useful for separating this species from its congener are hind wings with setal fringe, the pointed apex of the prosternal process ( Fig. 19 ), and the rufus coloration with testaceous elytral humeri and elytral apices.

Description. Holotype Male. Body elongate, subparallel, dorsum moderately convex ( Fig. 9 ). Length, 0.90 mm; greatest width, 0.45 mm. Dorsal surface sparsely setose. All appendages testaceous. Pronotum reddish-brown; elytra dark drown with testaceous patches at humeri and apices ( Fig. 9 ). Ventral surface testaceous and densely covered with recumbent setae.

Head microreticulate. Eye hemispherical, separated by a distance three times the radius of eye. Antenna with sparse, short setae, apical antennomere spindle-shaped ( Fig. 11 ). Clypeus explanate laterally. Labrum rounded apically; surface with fine, sparse punctation and covered with sparse, golden setae ( Fig. 4 ). Lacinia and galea long; apical palpomere of maxillary palpus spindle-shaped ( Fig. 1 ). Labium apically with a brush short, flattened setae and short hair-like setae ( Fig. 2 ). Labial palpus set into a furrow at base of labium ( Fig 2 ). Apical palpomere of labial palpus broad and cylindrical, bearing a patch of sensilla at apex ( Fig. 2 ).

Pronotum 0.35 mm long, 0.30 mm wide, roughly as wide at base as at apex, widest point at posterior third, broadly convex, with two complete, strong, sublateral carinae; lateral edges convex; anterolateral angles acute, slightly explanate and slightly depressed behind each angle; posterolateral angles acute, slightly explanate; discal area free from impressions, covered with very sparse setae and fine, dense, shallow punctures, punctures more dense anteriorly ( Fig. 10 ).

Prosternum very long in front of procoxae, approximately two times as long as prosternal process; with sparse setae, coarsely microreticulate without sculpturing medially, with strong, sinuate longitudinal carinae extending anterior of procoxae. Prosternal process expanded posterior to procoxae, forming a diamond-shaped projection; lateral margins concave, with curve for reception of procoxae; apex broadly pointed ( Fig. 19 ). Mesoventrite with sparse setae, coarsely microreticulate ( Fig. 11 ). Metaventrite coarsely microreticulate posterior to mesocoxae, densely setose laterally, with long flattened setae, glabrous at center line; disc with distinct, deep, longitudinal groove medially. Procoxae and metacoxae moderately widely separated; mesocoxae slightly more widely separated ( Fig. 11 ). Legs long and slender. Femora glabrous. Protibiae, mesotibiae, and metatibiae ( Figs. 15 & 17 ) with cleaning fringe at apex. Tarsi tetramerous on all legs, claws long and stout ( Figs. 15 & 17 ).

Elytron with seven rows of weak, shallow punctures; punctures separated by a distance roughly six times the diameter of the puncture; intervals with fine, very sparse setae, smooth and without sculpturing ( Fig. 10 ); elytron with two carinae (sublateral carina in basal 0.77, lateral carina reaching elytral apex), with dense setae of plastron lateral of lateral carina; elytral plastron setae long, (ca. 0.2 mm), with short lateral projections on the entire length of the seta ( Fig. 21 ). Hind wing with long setal fringe. Lateral margin of elytron with fringe of hooked setae ( Fig. 20 ). Elytral interior with patch of cuticular processes distally ( Fig. 16 )

Abdomen with five ventrites; cuticle densely covered with setae, with glabrous patch medially. First ventrite with intercoxal process broadly, shallowly depressed and distinctly carinate adjacent to metacoxae; carinae extending longitudinally behind metacoxae for half the length of ventrite; area posterior to metacoxae coarsely microreticulate. Second ventrite of male with two ventrally produced sensilla medially. Last visible ventrite broadly rounded, with lateral hook-like projections ( Fig. 11 ).

Aedeagus as illustrated, elateriform, median lobe of aedeagus 1.5 times as long as wide ( Fig. 5 ).

Female. Externally similar to male (tend to be larger in size), lacking two ventrally produced tubercles (sensilla) medially on second abdominal ventrite. Ovipositor as illustrated; Gonostylus with row of stout teeth laterally, with single seta between each tooth ( Fig. 6 ).

Intraspecific Variation. This species varies widely in coloration, with most individuals displaying strong testaceous markings on elytral humeri and apices, while others display a more uniform color pattern. The species also varies in size, from 0.9–1.2 mm long.

Etymology. The specific epithet, “ tetramera ” is a reference to the tarsal formula of members of this species, which is 4–4–4, in contrast with the all other known members of the family Elmidae , which have a 5–5–5 tarsal formula.

Habitat. The specific microhabitat for this species is unknown, as they were collected at a UV light approximately 30 m from the Sipaliwini River ( Short and Kadosoe 2011). The specimens were collected in a blacklight trap along with several hundred other elmid specimens comprising seven different genera.

Figures

FIGURES 1 – 4. Elachistelmis tetramera, n. sp.: 1. Maxilla; 2. Labium; 3. Mandible; 4. Labrum. Scale bar = 0.05 mm.

FIGURES 5 – 8. Elachistelmis tetramera, n. sp.: 5. Male genitalia, ventral view 6. Female genitalia, ventral view. Elachistelmis sipaliwiniensis, n. sp.: 7. Male genitalia, ventral view 8. Female genitalia, ventral view. Scale bar = 0.1 mm.

FIGURES 9 – 14. Elachistelmis tetramera, n. sp.: 9. Habitus, dorsal view, showing coloration; 10. Habitus, dorsal view, SEM; 11. Habitus, ventral view. Scale bar = 0.5 mm. Elachistelmis tetramera, n. sp.: 12. Habitus, dorsal view, showing coloration; 13. Habitus, dorsal view SEM; 14. Habitus, ventral view. Scale bar = 0.6 mm.

FIGURES 15 – 21. Elachistelmis tetramera, n. sp.: 15. Mesotarsus; 16. Interior of elytron, showing spines; 17. Metatarsus; 18. Head, vental view; 19. Prosternum; 20. Lateral border of elytron; 21. Elytron, showing long tuberculate setae of dorsal plastron.