Symmela instabilis Erichson 1835
Creators: name: Pacheco, Thaynara L.
name: Wipfler, Benedict
name: Monné, Marcela L.
name: Ahrens, Dirk
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Melolonthidae
Symmela
Symmela instabilis

description: Symmela instabilis Erichson, 1835
(Figures 13, 14, 30 (m), 32(d))
Symmela instabilis Erichson, 1835: 262 (original description); Blanchard 1850: 84 (catalogue)
Symmela instabilis instabilis: Burmeister 1855: 132 (revision); Harold 1869: 1126 (checklist); Frey 1973: 321 (key); Evans 2003: 48; Evans and Smith 2005: 30, 2007: 30, 2009: 31 (checklist)
Type material examined
Lectotype (here designated). ♂ ‘24970/ instabilis Er. Brasil. Virm./ Typus’ (ZMHB). Paralectotypes: 1 ♂ ‘24971/ Brasil / var./ Typus/ Symela instabilis Er. [typewritten]’ (ZMHB), 2 ♀♀ ‘24971/ Brasil / Typus / Symela instabilis Er. [typewritten]’ (ZMHB), 1 ♂, 2 ♀♀ ‘24970/ Brasil Vrmnd./ Typus/ Symela instabilis Er. [typewritten]’ (ZMHB).
Additional material examined
1 ♂, 1 ♀ ‘Brasilia Schaum’ (ZMHB), 1 ♂ ‘ Symmela Brésile 1/2’ (MNHN), 1 ♀ ‘ Symmela Brésile 1/2’ (MNHN).
Erroneous record: 1 ♂ ‘ Mexique / Symela sp./ Mus. Paris’ (MNHN).
Redescription
Length: 6.1 mm. Elytral length: 3.5 mm. Width: 3.4 mm. Head black, dull and shiny, with erect, sparse setae. Labroclypeus as wide as frons, subtrapezoidal; surface flat; plain, without an anterior concavity on each side; anterior margin straight, not elevated, with a rim of dense, short setae behind anterior margin; lateral margin not incised anteriorly; punctation of surface posteriorly dense; suture between labrum and clypeus invisible. Smooth area in front of eye distinctly separated from frons by a suture. Frons anteriorly flat, punctation irregular, dense. Ocular canthus with terminal setae, ratio of length of ocular canthus/eye diameter: 1/3. Eyes evenly spherical, ratio of diameter/interocular width: 0.57. Antenna with eight antennomeres. Antennal club with three antennomeres, blackish, straight; width of antennal lamella equal to width of antennomeres of funiculus; apical lamella subequal to basal and median ones; length ratio of antennal club vs remaining antennomeres combined: 1/1.1; length ratio of third vs fourth antennomere: 1/2; fourth antennomere without lateral projection; length ratio of fifth vs fourth antennomere: 1/5. Labrum anteriorly bluntly angled on each side, concave at middle. Setae on mentum moderately dense.
Head and pronotum with copper iridescent shine. Pronotum unicoloured, dull but iridescent, black; widest at base, width subequal to width of elytral base at humerus; anterior marginal line not interrupted medially, posterior marginal line absent; lateral margin not serrated, generally bent at middle, otherwise straight, behind anterior angles convex, posteriorly straight; setae of lateral margin sparse; basal margin evenly curved; transverse impression beside basal margin absent; anterior angles not produced, blunt; antero-lateral and postero-lateral angles not flattened dorso-ventrally; posterior angles blunt; surface with median longitudinal impression present over entire length of pronotum and two longitudinal furrows on each side, punctation on disc moderately dense, simple and fine, without well-defined impunctate areas. Scutellum without punctures.
Elytra unicoloured, black; surface iridescent, without setae and microsculpture; striae and intervals distinct; punctation between striae sparse, diameter of punctures compared to those of striae smaller; intervals flat; posterior edge convex; apical margin chitinous, without microtrichomes.
Abdomen: sternites flat in sagittal plane; lateral carina absent; first visible ventrite with row of setae on posterior edge; second visible ventrite with row of setae in medial region; basal ventrites medially with half length as laterally; ultimate and penultimate apical ventrites simple and flat; apical ventrite short (as long as preceding ventrite); penultimate apical ventrite with row of setae like preceding one; beside the robust row of setae, almost glabrous. Pygidium weakly convex.
Legs yellow. Ratio of length of metepisternum/metacoxa: 1/1.43. Metacoxa entirely plain, without elevated lateral longitudinal carina. Metacoxa with longer lateral bristles. Metacoxa, setae on basal surface present, posterior margin glabrous. Metafemur with posterior margin straight. Metatibia widest at apex; ratio of width/ length: 1/4.31; dorsal margin not carinated, smooth; interior surface more or less glabrous; median longitudinal punctation present on interior surface; interior margin of apex sharply and deeply truncate towards ventral margin; punctation on entire lateral face present; beside dorsal margin without a row of robust setae along entire length; basal group of spines reduced to a single robust spine; distal groups of spines disposed at two-thirds of metatibia length; ventral margin not serrated. Dorsal surface of tarsi glabrous, with dense punctures. Length ratio of dorsal tibial spur/first metatarsomere: 1/2. Metatarsi at apex weakly widened; first tarsomere straight, its length subequal to second and third tarsomeres combined; laterally not carinate; ventral margin serrated; ventral setose, ventral setae standing in a narrow line, robust and sparse, mainly in apical half of tarsomeres; medial face glabrous. Protibia with three indistinct, equidistant teeth; third basal tooth smaller than medium tooth; spur straight. First protarsomere straight, its length subequal to second and third combined; width ratio of first protarsomere to second protarsomere: 1.5/1; second protarsomere enlarged; third and fourth protarsomere elongate and narrow (distinctly longer than wide); fifth protarsomere circular in cross section, subequal to fourth protarsomere. Protarsal claws asymmetrical, shape of inner protarsal claw bifid, apex of basal tooth of inner protarsal claw convex.
Aedeagus: Figure 13 (d–e).
description: Published as part of Pacheco, Thaynara L., Wipfler, Benedict, Monné, Marcela L. & Ahrens, Dirk, 2022, The genus Symmela Erichson, 1835 (Coleoptera, Scarabaeidae, Sericini): taxonomy and phylogenetic analysis, pp. 607-705 in Journal of Natural History 56 (9 - 12) on pages 650-653, DOI: 10.1080/00222933.2022.2084649, http://zenodo.org/record/7012522