Adamas hukawngensis, Chen & Zhang, 2020

Chen, Xin-Yu & Zhang, Hua-Chuan, 2020, A new fossil record of Lymexylidae (Insecta: Coleoptera) from mid-Cretaceous amber of northern Myanmar, Zootaxa 4878 (1), pp. 195-200 : 196

† Adamas hukawngensis sp. nov.

( Figs 1–3 )

Etymology. The specific epithet is derived from the Hukawng Valley in northern Myanmar and is a reference to the location discovered of the specimen.

Type material. Holotype: male, in Burmese amber, CSCLRCAB100180.

Diagnosis. As for the genus.

Description. Male. Body length from anterior margin of frons to abdominal terminal 6.0 mm; elongate, nearly parallel-sided, moderately dorsoventrally flattened ( Fig. 1 ); lightly sclerotized; clothed in fine setae; legs long, thin. Head ( Fig. 2 A−B): ovate, length about 1.5X width, narrowed behind eyes, forming "neck"; eyes ( Fig. 2 A−B; e), entire and large, separated by less than single eye width, with stout intrafacetal setae; epicranial pit absent; antennae 11-segmented, with flagellum pectinate ( Fig. 2 C−D), rami of segments 3-11 approximatly 0.69 mm; scapus ( Fig. 2D; I ) short, 3/4 as long as pedicellus ( Fig. 2D ; II); antennal segments III−XI ( Fig. 2D ; III−XI) relatively long, almost equal in length; maxillary palp organ ( Fig. 2F ; mp) present, multi-branched, with two primary branches and parallel secondary branches forming a basketlike structure; maxillary palpus 4-segmented, segment IV ( Fig. 2F; p IV) elongate, with numerous apical sensilla. Thorax: pronotum length 0.95 mm, width 0.56 mm; pronotum slightly narrower than head, with mesal longitudinal depression, posterior and anterior widths equivalent (i.e., not constricted); scutellum ( Fig. 2H; s ) lozenge-shaped, with longitudinal median groove. Legs: long, thin, with dense shallow punctures and short, fine setae; portion of prothoracic leg lost, tarsal formula?-5-5, tibial spur formula?-0- 0. Each elytron ( Fig. 2 G−H) but slightly shortened, not covering abdomen; lightly sclerotized, with dense, shallow punctures and long, fine setae. Each metathoracic wing ( Fig. 3 B−C): large, membranous, not covered by elytron at rest, folded longitudinally only; venation only partially observed; C+Sc+R as well as r-m crossvein fragmentary, radius (R) fused with C + Sc at about middle; radial cell and radial crossvein absent. Metendosternite ( Fig. 3A ): furcal stalk long, parallel sided. Abdomen: flat in form, with seventh sternite visible; tergites and sternites wider than long; segments IV-VII similar in form, VII smaller than VI; VII forms circumgenitalic capsule; length 2.5 mm excluding genitalia, width at most 0.83 mm on IV segment. Male genitalia: lateral lobes ( Fig. 3E & 3G ; ll) symmetrical; abdominal segment IX of male symmetrical; abdominal sternite VIII of male without large setose pads; median lobe ( Fig. 3G ; ml) large relative to lateral lobes.

Remarks. The new species is distinguished from all recent and extinct genera of Lymexylidae by the lozengeshaped scutellum with a longitudinal median groove (that of Cratoatractocerus ( Wolf-Schwenninger, 2011) bears two longitudinal ridges plus a slightly grooved meson). The following characters are of diagnostic value: lengthened longitudinal oval-shaped head; pectinate antennae the same as “flabellate” morphs in Hylecoetus flabellicornis ( Schneider, 1791) but unlike all other lymexylids; huge eyes that occupy vast parts of the head surface and are strongly approximate dorsally (eyes large, ovate, conspicuous, occupying much of both the dorsal and ventral surfaces of the head in Atractocerus ); each elytron slightly shortened, not covering all the parts of the abdomen (elytra very short, exposing most abdominal terga in Atractocerus ); large median lobe relative to lateral lobes.

Female. Unknown.

Figures

FIGURE 1. Adamas hukawngensis, holotype (CSCLRCAB100180). A. habitus, dorsal view. B. habitus, ventral view. Scale bars: 1.0 mm.

FIGURE 2. Adamas hukawngensis, holotype (CSCLRCAB100180). A. dorsal image of head. B. Drawing of dorsal head. C. Image of antenna. D. Drawing of antenna. E. Image of maxillary palp organ. F. Drawing of maxillary palp organ. G. Image of elytron and scutellum. H. Drawing of elytron and scutellum. Abbreviations: 1º = primary branch; 2 º = secondary branch; I, II, III-XI = scapus, pedicellus, antennal segments III−XI; e = eyes; mp = maxillary palporgan; p IV = palpomere IV; S = scutellum. Scale bars: A–B = 0.1 mm; C–H = 1.0 mm.

FIGURE 3. Adamas hukawngensis, holotype (CSCLRCAB100180). A. Metendosternite. B. Image of metathoracic wing. C. Drawing of metathoracic wing. D. Image of male genitalia, dorsal view. E. Drawing of male genitalia, dorsal view. F. Image of male genitalia, lateral view. G. Drawing of male genitalia, lateral view. Abbreviations: ll = lateral lobes; ml = median lobe. Scale bars: A–C = 1.0 mm; D–G = 0.2 mm.