Ytu nyx, Sampaio & Ferreira-Jr, 2018

Sampaio, Brunno Henrique Lanzellotti & Ferreira-Jr, Nelson, 2018, Five new species of Ytu Reichardt (Coleoptera: Myxophaga: Torridincolidae) and new records from Brazil, Zootaxa 4402 (3), pp. 508-524 : 517-519

Ytu nyx sp. nov.

( Fig. 4 )

Diagnosis. Middle line of pronotum with a narrow longitudinal impression from posterior margin to first third; a small impression on each side of medial impression on first third, and a sublateral impression on first third. Elytron with edges flattened; elytral formula 8d + 0a + 1sl / 0d + 0sl; nine complete stria formed by a rows of punctures; elytral intervals with iridescent microscales and feebly raised; striae forming sulci. Male genitalia with long parameres (half length of phallus); phallus narrow in lateral view; dorsal surface convex up to apical fourth, where it is slightly convex and presents small setae; feebly widened digitiform apex (in relation to phallus width), bearing long setae on dorsal face.

Description: Holotype. Antennae black; dorsal surface shining black ( Fig. 4a ); ventral surface dark brown ( Fig. 4b ); legs dark brown, darker distally. Measurements: total length: 1.70 mm; maximum head width: 0.30 mm; pronotal length: 0.32 mm; maximum pronotal width: 0.48 mm; elytral length: 1.07 mm; maximum elytral width: 0.40 mm.

Labrum ( Fig. 4c ) slightly longer than wide; anterior margin slightly convex with denticles; anterolateral angles arcuate with claviform setae; medial region with a process; lateral margin slightly arcuate; surface smooth and glabrous on posterior third and medial region; other regions of labrum with sparse punctures bearing setae. Clypeus ( Fig. 4d ) with anterior margin arcuate; anterolateral angles arcuate; lateral margin oblique; posterior margin arcuate with posterolateral angles projected. Head surface with iridescent microscales, except for a narrow band near the pronotum; supra-orbital carina extending from clypeus to posterior margin of eyes; region beside each carina depressed; head medially feebly raised. Antenna with nine antennomeres; last antennomere as long as VI–VIII combined. Mandibles asymmetrical ( Figs. 4e–f ); left mandible with two incisors—one immobile (distal), one movable (proximal); distal incisor with three denticles on inner margin; outer margin strongly arcuate on medial third; right mandible similar to left one, bearing only an immobile incisor. Maxilla with galea and lacinia fused into a mala; mala with apical cuticle teeth; claviform setae on inner margin; maxillary palp four-segmented, second article twice as long as first one; third article 1.5× longer than second one; apical one very small.

Anterior margin of pronotum ( Fig. 4a ) sinuate, medially protuberant; anterolateral angles strongly projected; lateral margin arcuate; greatest width at middle third; posterior margin bisinuate, medially more pronounced than at the posterolateral angles; posterior margin with single small medial incision; middle line of pronotum with a narrow shallow longitudinal impression extending from posterior margin to first third; a small round impression on each side of medial longitudinal impression on first third; sublateral round impression, smaller than the medial, on first third; posterolateral angles with shallow impression on the lateral thirds of pronotum. Anterior margin of elytron ( Fig. 4a ) arcuate; lateral margin arcuate, converging to acute apex; edges of elytron explanate; elytral formula 8d + 0a + 1sl / 0d + 0sl; striae formed by row of punctures, sublateral stria beginning in middle fifth; elytral intervals with iridescent microscales and feebly raised, so that the striae form sulci. Epipleuron broad and smooth on anterior two fifths. Hind wings reduced ( Fig. 4h ); marginal fringe with very short setae, beginning just distal the radial hinge (which is weakly marked); RA3+4 beginning near radial hinge, extending toward the anterior margin, just distal to a convexity on anterior margin of wing; RA3+4 borders a pigmented area; RA4 not visible; RP weakly marked, visible briefly, near basis; r1 short, oblique, not crossing any vein; r4 oblique; MP 1+2 strongly marked, angulate on medial hinge, crossing rp-mp1 and rp-mp2 (which is weakly marked), forming oblong cell; Cu vein almost parallel to MP1+2, extending toward posterior margin, ending at AA3, which extends to posterior margin; AA3+4 present only near base; anal lobe very small and narrow. Anterior margin of prosternum arcuate and crenulate ( Fig. 4b ); prosternal carinae slightly oblique; prosternal process narrower between procoxae, widening toward the posterior margin; posterior margin of prosternal process bisinuate, oblique laterally, and slightly concave medially. Anterior margin of mesoventrite feebly projected, with a medial gibbosity which fits into an internal concavity on prothorax; posterior margin truncate between the middle coxae. Metaventrite depressed medially, but without a conspicuous discrimen; metaventral carinae and tubercles absent. Metacoxae with posterior margin slightly projected over trochanter and femur and feebly serrated; femora with a fringe of long setae on anterior face; tibiae with a fringe of small setae on anterior and posterior face; tarsus with four articles; third tarsomere 1.5× longer than first and second together; fourth tarsomere as long as twice the third one.

Abdomen with visible plastron, covering the whole surface; ventrites 1¯4 with posterior margin microserrate; posterolateral angles of ventrites acutely projected, except for the last; first ventrite without medial carina. Male genitalia ( Figs. 4i –j ) with long parameres, reaching half length of phallus; pair of apical setae on each paramere, one-third length of paramere. Phallus narrow in lateral view; dorsal surface convex up to apical fourth, where it presents a feeble concavity; concave area bears small setae; phallus with digitiform apex, slightly wide, bearing long setae on dorsal face.

Female: unknown.

Variation. Total length: 1.70¯ 1.91 mm; maximum head width: 0.30¯ 0.33 mm; pronotal length: 0.32¯ 0.40 mm; maximum pronotal width: 0.48¯ 0.58 mm; elytral length: 1.05¯ 1.12 mm; maximum elytral width: 0.40¯ 0.43 mm.

Comparative notes. Ytu nyx sp. nov. is similar to species of the Ytu demeter group, because the lack of carina on ventrite 1 and the total length greater than 1.4 mm. Ytu nyx sp. nov. is especially similar to Ytu godoyi Reichardt & Vanin because it presents nine striae on elytron. These two species differ from each other by the following characteristics: Ytu nyx sp. nov. has supra-orbital carinae complete (interrupted abruptly on Y. godoyi ); this new species lacks metaventral tubercles and carinae ( Y. godoyi has metaventral tubercles and presents faded carinae); the male genitalia of Ytu nyx sp. nov. resembles that of the Ytu phebo group (Reichardt & Vanin 1977, figs. 13̄17).

Etymology. This species is named after the Greek mythological entity Nyx, personification of the night, in reference to its dark color and its resemblance to Y. thanatos sp. nov. and Y. hypnos sp. nov. (in Greek mythology Nyx is mother of Thanatos and Hypnos).

Type material: Holotype. Male. Brasil, Espírito Santo, Dores do Rio Preto, Pedra Menina, Parque Nacional do Caparaó , Rio São Domingos , Cachoeira do Aurélio , 20°28’56.5”S; 41°50’14.6”W, 1814m alt., 6.I.2013, Col.: Sampaio, B.H.L. [ DZRJ 5647 ] ; paratype: 1 male— Brasil, Espírito Santo, Dores do Rio Preto, Pedra Menina, Parque Nacional do Caparaó , Cachoeira Sete Pilões , 20°28’56.8”S; 41°49’50.3”W, 1869m alt., 06.I.2013, Col.: Sampaio, B.H.L. [ DZRJ 5648 ] ; 1 male— Brasil, São Paulo, Atibaia , 11.III.2006, Col.: Roque, F. [ DZRJ 5649 ] .

Figures

FIGURE4. Ytunyx sp. nov.: a̅b: habitus, a)dorsal view,b) ventral view; c) labrum,dorsal view; d) clypeus,dorsal view; e̅f: mandibles, dorsal view, e) left mandible, f) right mandible; g) right maxilla, dorsal view; h) right hind wing, dorsal view; i̅j: aedeagus, i) dorsal view, j) lateral view.(Scale bars:a̅b: 0.5 mm; c̅g: 0.05 mm; h: 1 mm; i̅j: 0.2 mm).