Ytu thanatos, 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 : 509-511

Ytu thanatos sp. nov.

( Fig. 1 )

Diagnosis. Surface strongly sculptured; pronotum with sublateral carina, three pairs of round depressions on anterior third and three large depressions on posterior third, forming a skull-like raised area medially; depressed area iridescent and raised area smooth. Elytral formula 12d(I-II,III-IV,V-VI,VII-VIII,IX-X,XI-XII) + 1a(aIX) + 1sl / 5d(III,V,VII,IX,XI) + 1sl(XIII); striae formed by foveolate rows of punctures grouped in pairs, except for the accessory stria (aIX) and the lateral stria. Male genitalia with parameres slightly longer than phallobase process, and phallus about five times as long as paramere, with relatively wide digitiform apex.

Description: Holotype. Antennae black; head and body surface black and iridescent in dorsal view ( Fig. 1a ); ventral surface dark brown ( Fig. 1b ). Measurements: total length: 1.65 mm; maximum head width: 0.30 mm; pronotal length: 0.37 mm; maximum pronotal width: 0.58 mm; elytral length: 1.02 mm; maximum elytral width: 0.52 mm.

Labrum subquadrate ( Fig. 1c ); anterior margin straight, with some small teeth, long and fine setae on anterolateral angles; medial process projected on anterior margin; lateral margins parallel; surface with sparse punctures bearing setae. Anterior margin of clypeus ( Fig. 1d ) slightly arcuate; anterolateral angles oblique; lateral margins subparallel; posterior margin arcuate with lateral angles feebly projected. Frons bearing a pair of lateral carinae from clypeal suture to the posterior margin of eyes, more conspicuous on anterior half; each carina with a depression on its medial side. Head surface rugose behind posterior margin of eyes. Antenna with nine antennomeres; last antennomere as long as antennomeres V–VII, bearing a pair of setae on ventral surface. Mandibles asymmetrical ( Figs. 1e–f ); left mandible with two incisive teeth—proximal movable, distal immobile; distal tooth without denticles on inner margin; outer margin of left mandible projected on basal half; right mandible similar to left one, except for the lack of a proximal incisive tooth. Galea and lacinia fused into mala ( Fig. 1g ); mala with apical cuticular tooth; maxillary palp with four articles; second article about two times as long as first one; third article 1.7× as long as second one; apical one very small.

Anterior margin of pronotum emarginate ( Fig. 1a ), with anterolateral angles pronounced; lateral margin convex, sinuate and crenulate (coarsely on anterior half); greatest width on posterior third; posterior margin oblique with a medial incision; small fine sparse setae inserted on a fold of posterior margin of pronotum. Surface of pronotum strongly sculptured; anterior third with three pairs of round depressions: one near each anterolateral angle, fading posteriad; one on each side of medial line; and one between these two impressions; posterior half with three large depressions: one medial, divided by a raised medial line; and one on each side, divided by a sublateral carina, which extends from posterior to anterior margin; depressions with iridescent surface and raised parts smooth. Scutellar shield very small; rounded on anterior margin and obovate on posterior margin. Elytron ( Fig. 1a ) with anterior margin sinuate with a small acute projection near humeral callus; lateral margin crenulate, converging to an acute apex; greatest width of elytra on the anterior third; elytral formula 12d(I-II,III-IV,V-VI,VII- VIII,IX-X,XI-XII) + 1a(aIX) + 1sl / 5d(III,V,VII,IX,XI) + 1sl(XIII); complete stria formed by foveolate rows of punctures, grouped in pairs, except for the accessory stria (aIX) and the lateral stria; striation easier to observe on ventral side of elytron; sublateral carina beginning on the second fifth of the elytra, extending to the apex between striae XII and XIII; epipleuron smooth, broader on anterior third of elytron. Hind wings developed ( Fig. 1h ); margin with fringe of long setae from radial hinge to the anterior part of the anal lobe; ScP and RA1+2 extending to the radial hinge; RA3+4 beginning near the radial hinge and extending toward the anterior margin, near a sinuosity on that margin, bordering a small pigmented area; RA4 very weakly marked, not parallel to RA3, fading before the margin; RP feebly marked, fading just after it begins; r1 very short, not connected to any vein; r4 obtuse, connecting RA3 to RP2 which is weakly marked and not reaching the margin; MP1+2 strongly marked, angulated at medial hinge, crossing rp-mp1 and rp-mp2 (forming the oblong cell); medial spur slightly shorter than rp-mp1, curved toward the posterior margin; Cu parallel to MP1+2, turning toward posterior margin, ending on the AA3; AA3+4 weakly marked; AA3 strongly marked, extending near to posterior margin; AP1+2 absent; AP3+4 strongly marked, bordering the posterior margin of the anal lobe which is relatively small and very narrow. Anterior margin of prosternum feebly concave and crenulate; lateral margin converging posteriad on the anterior two thirds; posterior third (prosternal process) with lateral margins divergent posteriad and posterior margin slightly sinuate and wider than anterior margin of prosternum; with deep central depression on posterior half of prosternum. Mesoventrite with anterior margin slightly emarginate, with a medial gibbosity which fits into an internal concavity on the prothorax; lateral margins subparallel; posterior margin truncate and two thirds as wide as anterior margin. Metaventrite with discrimen marked from posterior margin, almost reaching anterior margin; posterior third of metaventrite slightly raised, especially near discrimen; metaventral carina complete. Profemur with a row of fine setae on posterior face; protibia with fine and very short pubescence dorsally and with anteroventral fringe of small setae; tarsus with four tarsomeres; third tarsomere twice as long as first and second together; last tarsomere as long as the third one, with a long seta on ventral face; mesofemur with a row of fine setae on anterior face and a shallow concavity on posterior face to fit the tibia; mesotibia and tarsus similar to the first pair of legs; metacoxa with shallow concavity on posterior face to fit the metafemur; metatrochanter with a small tooth-like projection; metafemur with similar concavity to fit metatibia; metatibia and tarsus similar to the other legs.

First abdominal ventrite with a conspicuous medial carina fading near the posterior margin; ventrites 2¯5 with lateral margin raised with a fine pubescence. Male genitalia ( Fig. 1i –j ) with short parameres, slightly longer than phallobase process; each paramere with pair of apical setae, as long as the paramere; phallus about five times as long as paramere; lateral margins parallel on basal half, converging on apical half; apex digitiform, relatively wide.

Female: unknown.

Variation. Total length: 1.57¯ 1.65 mm; maximum head width: 0.30¯ 0.31 mm; pronotal length: 0.32¯ 0.37 mm; maximum pronotal width: 0.55¯ 0.58 mm; elytral length: 0.93¯ 1.03 mm; maximum elytral width: 0.43¯ 0.52 mm.

Comparative notes. Ytu thanatos sp. nov. is similar to species from the Ytu zeus group because of the presence of a carina on the first ventrite and its total length greater than 1.4 mm. It is especially similar to Y. cleideae Vanin because both have 13 striae on elytron. However, Ytu thanatos sp. nov. presents a different sculpture on pronotum and elytron, the pronotum having a group of depressions that form a skull-like raised area, not present on Y. cleideae, and the elytron of Ytu thanatos sp. nov. does not have even elytral intervals keeled like on Y cleideae (Vanin 1991, fig. 1). The male genitalia of these two species are completely different, being curved and abruptly bent downward at apex and forming an acute hook in Y. cleideae (Vanin 1991, figs. 2 and 4) and weakly curved but not forming a hook in Y. thanatos.

Etymology. This species is named after the entity Thanatos, the personification of death in reference to the skull-like surface of the pronotum.

Type material: Holotype. Male. Brasil, Espírito Santo, Castelo, Parque Estadual do Forno Grande, Afluente do Rio Caxixe , 20 °31’05.6”S; 41°05’09.0”W, 30.III.2011, Col.: Jardim, G.A.; Dumas, L.L.; Nessimian, J.L. [ DZRJ 5638 ] ; paratype: 1 male— Brasil, Espírito Santo, Domingos Martins, Parque Estadual da Pedra Azul , Córrego das Piscinas, 20°23'51.4"S; 41°01'23.9"W, 1236m alt. 01.IV,2011, Col.: Jardim, G.A. [ DZRJ 5639 ] ; 1 male— Brasil, Rio de Janeiro, Petrópolis, Fazenda Inglesa, BR-040, Cachoeira do Brazão 22°27’09.81”S; 43°12’21.6”W, 822m alt., 24.X. 2010, Col.: Moraes, C.; Ferreira-Jr, N.; Sampaio, B.H.L. [ DZRJ 5640 ] .

Figures

FIGURE 1. Ytu thanatos 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).