Silis (Silis) carsteni, Bukejs & Fanti, 2023

Bukejs, Andris & Fanti, Fabrizio, 2023, Two new fossil Silinae (Coleoptera, Cantharidae) from Baltic amber, Baltic Journal of Coleopterology 23 (2), pp. 331-339 : 334-337

Silis (Silis) carsteni sp. nov.

( Fig. 2 )

Type material. Holotype: GPIH no. 5203, CCGG no. 8702, (ex coll. Jonas Damzen JDC-12439); adult, female. A complete beetle with partially exposed metathoracic wings is included in a transparent, yellow amber piece with dimensions of 31× 16 mm and a maximum thickness of 5 mm; preserved without supplementary fixation. Syninclusions: few stellate Fagaceae trichomes.

Two new fossil Silinae ( Coleoptera , Cantharidae ) from Baltic amber

Type locality. Amber mine in Yantarny settlement, the Sambian Peninsula, the Kaliningrad Region, Russia .

Type stratum. Baltic amber; Middle– Upper Eocene ( Sadowski et al. 2017, 2020; Seyfullah et al. 2018; Bukejs et al. 2019; Kasiński et al. 2020).

Systematic placement. The specimen considered here was assigned to the genus Silis based on a combination of the following morphological characters: (1) the pronotum non-incised at lateral sides (incised in females of Podosilis ), with impressions (without impressions in Autosilis ), (2) abdomen with six visible sternites (seven sternites in females of Podosilis ), (3) tarsomere 4 wider than others tarsomeres (tarsomere 4 as wide as tarsomeres 1–3 in Eusilis ), (4) claws simple, internal claw with obtuse and small tooth basally (all claws with large denticle basally in Asiosilis ), and (5) the distal margin of ultimate tergite without conspicuous processes at lateral sides.

Differential diagnosis. A new species resembles Silis (s. str.) boninoi Fanti & M. G. Pankowski, 2022 (Baltic amber; male), but differs in flat and widely explanate pronotal lateral sides, pronotum widest basally (in contrast to pronotum widest in the middle in S. boninoi ), obtuse posterior pronotal angles (in contrast to acute triangular porterior pronotal angles in S. boninoi ), larger pronotum, different shape of antennomere 1, and elytra wider at humeri. Silis (s. str.) carsteni sp. nov. differs from Silis (s. str.) lombardii Parisi & Fanti, 2019 (Baltic amber; male) by the considerably smaller body size. A new species differs from Dominican amber species Silis (s. str.) hegnai Fanti & M. G. Pankowski, 2021 and Silis (s. str.) curleri Fanti & M. G. Pankowski, 2021 by distinctly smaller body size; and from Silis (s. str.) chiapasensis Wittmer, 1963 (described from Mexican amber) by the

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smaller body size and the longer elytra comparated to abdominal length.

Description. Body elongate-oval, flatened; sparsely covered with homogenous, short, semierect to erect setae; integument unicolorous dark brown (as preserved). Measurements: total body length 2.8 mm (from anterior margin of head to elytral apex); pronotum length 0.5 mm, pronotum maximum width 1.0 mm; elytra length 2.3 mm, elytra maximum width 1.3 mm, elytra width at base 1.0 mm.

Head partially covered by pronotum, small, short, transverse, covered with fine punctation, distinctly narrower than anterior margin of pronotum. Compound eyes rather small, nearly hemispherical, strongly prominent, inserted in upper and lateral parts of head. Mandibles falciform, simple. Maxillary palpi 4-segmented, unequal in length, terminal palpomere securiform. Labial palps 3-segmented, terminal palpomere securiform. Antennae inserted far from from inner margin of eyes, relatively short, extending about to middle of elytra, 11-segmented, filiform, all antennomeres covered with short, semierect setae; scape longest, strongly elongate, about 3.0× longer than wide, not particularly robust, curved, dorso-apically enlarged and sligthly protruding forward; antennomere 2 shortest, cylindrical, about 0.6× as long as scape; antennomeres 3–5 equal in size and shape, subcylindrical, dilated apically, 2.4× as long as wide, robust, about 1.2× as long as antennomere 2; antennomeres 6–10 sub-equal in size and shape, subcylindrical, dilated apically, 2.5× as long as wide, slightly shorter than antennomere 5; antennomere XI elongate oval with acute and long apex, about 3.5× as long as wide; relative length ratios of antennomeres 1–1 equal to 9:5:6:6:6:5:5:5:5:5:7.

336 Pronotum trapezoidal, strongly transverse, about 2.0× wider than long, widest in posterior one-fourth of its length, distinctly wider than head; punctation fine and sparse on disc and denser laterally; disc convex, with subtriangular impressions basally and suboval impressions anterolaterally; pronotal sides widely explanate. Pronotal anterior margin rounded medially; posterior margin slightly concave laterally and distinctly protruding medially forming wide lobe; lateral margins weakly rounded, non-incised, with two obtuse and small tooth (one at anterior angles and one near posterior margin). Anterior angles obtuse, rounded, slightly projecting; posterior angles obtuse. Prohypomera covered with fine punctation,

Scutellar shield subtrapezoidal, rounded apically, with fine punctation. Elytra at humeri wide and slightly narrower than pronotum, while in posterior one-third of elytral length wider than pronotum, elongate-oval, 1.8× longer than wide, subparallel-sided in anterior two-thirds and strongly widened in posterior one-third, rounded apically, completely covering abdomen; humeri distinct; humeral costae sharp, distinct in anterior two-thirds of elytral lenght elytral punctation small and rather dense, distance between punctures apparently lesser than diameter of one puncture.

Metaventrite wide, with rounded posterior margin, covered with fine punctation; disc convex. Metathoracic wings fully developed, completely covered by elytra.

Legs rather long, slender, pubescent. Pro- and mesocoxae subconical, robust, metacoxae narrow, strongly transverse. Trochanters elongate with rounded apex. Femora slightly enlarged, flattened, slightly curved. Tibiae subcylindrical, with apical spur, nearly as long as femora. Tarsal formula 5-5-5; tarsomere 1 longest, elongate; tarsomere 2 slightly shorter than tarsomere 1; tarsomere 3 subtrapezoidal, slightly dilated apically, wider than previous ones, shorter than tarsomere 2; tarsomere 4 widest, deeply bilobed; tarsomere 5 subcylindrical, strongly elongate, slender, curved. Pretarsal claws simple, internal claws with obtuse and small basal tooth.

Abdomen with six visible sternites (ventrites), covered with fine punctation; ultimate sternite wide, transverse, with emarginated posterior margin; ultimate tergite concave apically, longer and narrower than ultimate sternite.

Etymology. The specific epithet is a patronym; the new species is named in honor of Mr. Carsten Gröhn (Glinde, Germany), an enthusiast and specialist in Baltic amber.

Remark. The lateral margins of pronotum without long lobes or teeth, the proportions of elytra (lenght/widht ratio), widely explanate elytral margins, relatively short anttenomeres, as well as ultimate abdominal sternite wide and emarginated apically indicate that the specimen is female.

Figures

Fig. 2.Silis(Silis) carsteni sp. nov., holotype, No 5203 [GPIH]: A – habitus, dorsal view; B – habitus, ventral view.