Synarmostes humilis Fairmaire, 1893

Ballerio, Alberto, 2021, The Ceratocanthinae of Madagascar and Comoro Islands: a revision of the genera Synarmostes and Goudotostes, and of the flightless Philharmostes, with description of 64 new species (Coleoptera: Scarabaeoidea, Hybosoridae), Fragmenta entomologica 53 (2), pp. 105-282 : 157-158

Synarmostes humilis Fairmaire, 1893

( Figs 21 a-d, 17 c-d, 29 a-d, 36)

Fairmaire 1893: 530 (description); Alluaud 1900: 245 (catalogue); Arrow 1912: 45 (catalogue); Paulian 1937: 131 (catalogue, key); Paulian 1978a: 71 (catalogue); Ocampo & Ballerio 2006: 190 (listing).

Type locality: “ Mayotte ” .

Material examined: Holotype, ♂ ( MNHN) : / Holotype / Muséum Paris 1906 Coll. Léon Fairmaire / Synarmostes humilis [unreadable] / Mayotte Ed. Marie /. Other material examined (not belonging to the type series): 169 specimens [20 ♂♂ dissected] (130 in CASC and 39 in ABCB): / Mayotte: Mont Combani 25-28 November 2007 elev. 370 m 12°48’23”S 045°09’11”E Calif. Acad. of Sciences coll. B. L. Fisher et al. sifted litter rainforest collection code: BLF18636 /. 1 ♀ ( CJBH): / COMORES Mayotte Mt Combani entre Vahibé / Combani IX.1998 J. Sudre leg. Tamisage d’humus en forêt humide /.

Diagnosis. Synarmostes humilis can be differentiat- ed from all other species of Synarmostes by the following combination of characters: a) small size, b) ventral ocular area small-sized, c) dorsal ocular area present, d) dorsal setation present (20×), e) flightlessness, f) carinae of elytral apical third regular (without tubercles or other irregularities), g) scutellum smooth, without punctation, h) pronotum with an anteromedian area smooth, i) punctation of pronotum and elytra sparse, j) parameres with apex enlarged and rounded (more rounded than in S. benaraensis ) in lateral view, k) elytral inferior sutural stria not reaching humeral area. Synarmostes humilis belongs to the humilis group of species and can be distinguished from the other species of the group only with the examination of the aedeagus, which has the distinctive shape indicated under letter j) above.

Description. Size: HL = 0.9 mm; HW = 1.1 mm; PL = 1.00 mm; PW = 1.8 mm; EL = 1.8 mm; EW = 1.8 mm. Overall morphology as in generic diagnosis. Small-sized flightless Synarmostes . Body strongly convex. Dark-brown with bronze sheen, shiny, dorsum with setigerous punctures bearing a medium-sized fine seta (20×), underside, tarsi and antennae reddish-brown, setation yellowish-brown. Head: W/L ratio = 1.37, clypeal apex obtuse, apical projection distinctly protruding and sharp; dorsal ocular area small, interocular distance about 17 times the maximum width of dorsal ocular area, ventral ocular area small; head dorsal surface with a small discal area smooth, sides of smooth area covered by sparse medium-sized comma-shaped punctation mixed to some horseshoe-shaped punctures with opening directed inwards. Fore margin with one or two transverse large comma-shaped punctures. Interpunctural distance of punctures irregular: half their width or once or twice larger than their width. Vertex smooth with one transverse impressed irregular line interrupted in the middle. Pronotum: subrectangular (W/L ratio = 1.76) with ellip- tical base, regularly convex, pronotal surface with disc almost smooth, with only some sparse shallow simple punctures, sides covered by medium-sized sparse shallow transverse comma-shaped punctures, each one having a simple setigerous puncture inside. Interpunctural distance shorter than punctural width. Scutellum : almost completely smooth. Elytra: longer than wide (W/L ratio = 0.82); subrectangular (dorsal view); inferior sutural stria ending before humeral area; humeral callus indistinct; elytral surface regularly convex, uniformly covered by sparse shallow punctation. Interpunctural distance once to four times the maximum width of punctures. Punctures transverse comma-shaped near base and sides of elytra, becoming horseshoe-shaped punctures with opening directed backwards on medial third, each one having a simple setigerous puncture inside. Elytral distal third with four raised longitudinal carinae (excluding elytral suture) sometimes with a longitudinal impressed irregular line between them. Wings: flightless (apterous). Male genitalia: aedeagus (L = 1.1 mm) with parameres as in Figs 29 a-c, spiculum gastrale (L = 0.9 mm) as in Fig. 29 d .

Etymology. Latin adjective in the nominative singular, meaning “humble”. Fairmaire did not provide the etymology of this species name. Probably he wanted to refer to the small size and nondescript appearance of this species, compared to the larger and more imposing appearance of Synarmostes tibialis .

Distribution and habitat. The specimens here attributed to the species have been found in two localities of Mount Combani in the centre of the island, one of the four main mountain ranges of Mayotte. Specimens were collected by sifting leaf litter in rainforest.

Figures

Fig. 21 – Synarmostes humilis (Mont Combani), a, dorsal view of distended specimen; b, ventral view of rolled up specimen; c, dorsal view of rolled up specimen; d, lateral view of rolled up specimen; Synarmostes benaraensis sp. nov., e, dorsal view of distended paratype; f, ventral view of rolled up paratype; g, dorsal view of rolled up paratype; h, lateral view of rolled up paratype.

Fig. 29 – Aedeagi and spicula gastrales, a, Synarmostes humilis, holotype. b–d, Synarmostes humilis (Mont Combani); e–g, Synarmostes benaraensis sp. nov., paratype; h–j, Synarmostes chonguimontis sp. nov., paratype; k–m, Synarmostes dapaniensis sp. nov., paratype; n–p, Synarmostes karthalaenisis sp. nov., paratype; q–s, Synarmostes grinteri sp. nov., paratype.