Silis (Silis) boninoi FANTI & M. G. PANKOWSKI, 2022

Fanti, Fabrizio & Pankowski, Maximilian G., 2022, A new fossil Silis Charpentier, 1825 from Baltic amber (Cantharidae, Silinae, Silini), Zootaxa 5195 (1), pp. 87-91 : 88-90

Silis (Silis) boninoi FANTI & M. G. PANKOWSKI sp. nov.

( Fig. 1 )

Description. Adult, winged, male. Body length: 2.7 mm; elytra: approximately 2.4 mm long, and 1.0 mm wide at apex. Entirely blackish-dark brown.

Head large, slightly narrower than pronotum, smooth, equipped with several long setae, largely covered by pronotum. Eyes rounded and protruded, wide, inserted in upper and lateral part of the head. Maxillary palpi 4- segmented, unequal in length with last palpomere very elongated and securiform. Labial palps 3-segmented with last palpomere securiform. Antennal insertions and eyes not juxtaposed, antennae surpassing two-thirds of the elytra, 11-segmented, filiform, each antennomere covered with several setae; scape elongated, slightly club-shaped; antennomere II (pedicel) short, about 2.1 times shorter than scape; antennomeres III–V subequal in length, longer than antennomere II, rather robust; antennomeres VI–IX subequal in length, slightly longer than antennomeres III–V; antennomere X very slightly shorter and more slender than previous ones; antennomere XI filiform, oblong with extremely thin and pointed apex. Pronotum strongly transverse, surface undulating with concavities (pores) and equipped with sparse long setae, apparently without punctuation; anterior margin curved and protruding in the middle; sides strongly sinuous, with two very short processes on each side: Posterior processes are thicker and wider than anterior ones and rounded apically; anterior processes are shorter than posterior ones and rounded apically; posterior margin irregular and sinuous with two expansions in the middle. Scutellum triangular with rounded apex. Elytra wider than pronotum, elongated and surpassing last abdominal segments, enlarged at humeri and apex, restricted in middle, apex strongly rounded, surface with very superficial punctation and several very long setae. Posterior wings transparent, completely covered by elytra but just barely shorter than them. Metasternum very elongated with a strongly rounded posterior margin, abdominal segments transverse and pubescent. Legs relatively short, robust and strongly pubescent; coxae massive; trochanters elongated and triangular-shaped with rounded apex; femora enlarged and slightly curved; tibiae cylindrical, with one apical and robust spur, protibiae as long as profemora, mesotibiae slightly shorter than mesofemora, metatibiae just slightly shorter than metafemora. Tarsal formula 5-5-5; first tarsomere elongated; second tarsomere about 1.2 times shorter than first; third tarsomere triangular and shorter than tarsomere II; fourth tarsomere deeply bilobed at sides; fifth tarsomere very elongated, slender, flat and curved; claws simple without basal tooth.

Note. Female unknown. The specimen is a male, defined on the basis of long antennae and lateral sides of pronotum toothed. Sexual dimorphism is supposed because females of the genus Silis are characterized by a pronotum with sides without appendages or with very small teeth, and have shorter antennae and a wider abdomen than males.

Etymology. Named in honor of Enrico Bonino for donating the described specimen, photographing it and kindly giving us access to it.

Holotype. Male , in Baltic amber, deposited at the Back to the Past Museum, Cancún, Mexico with accession no. BPM-1111.

Type locality. Yantarny mine, Sambian Peninsula, Kaliningrad Region, Russia.

Type horizon. Middle Eocene: Bartonian-Priabonian (45.0–38.0 Mya).

Syninclusions. A few botanical fragments (trichomes).

Systematic placement. The specimen is clearly a new species belonging to the subfamily Silinae and to the genus Silis ( Brancucci 1980; Kazantsev 1997) based on its maxillary palpi sub-equal in length with their last palpomere securiform, elytra elongated, tarsomeres IV wider than other tarsomeres, pores on the anterior part of the pronotum, the internal claw simple, tibial spurs conspicuous and the lateral section of its pronotum having two lobes on each side.

Genera that appear most similar to Silis are distinguished by a few different characters. The genus Podosilis has a complex pronotal armature at the sides and a cleft outer claw in males ( Kazantsev 1997, 2019, 2020). Autosilis features the anterior half of its mesonotum smooth without clear pores, and the anal ring in the male has a tergite and sternite that are roughly equally wide ( Kazantsev 1997).

Differential diagnosis. Silis boninoi sp. nov. differs from Silis lombardii Parisi & Fanti, 2019 (from Baltic amber) based on the new species’ pronotum that is much more transverse and with shorter pronotal lobes on its sides, and by the new species’ significantly smaller size: 2.7 mm vs. 5.2 mm for S. lombardii ( Parisi & Fanti 2019) . In addition, Silis chiapasensis Wittmer, 1963 (found in Mexican Chiapas amber) differs based on its pronotum that is deeply incised at the sides and its lobes that are more curved and longer than on the new species ( Wittmer 1963). Finally, Silis curleri Fanti & M. G. Pankowski 2021 and Silis hegnai Fanti & M. G. Pankowski 2021 (both from Dominican amber) have a very different pronotal shape, with lobes that are longer and more curved, and a less transverse pronotum ( Fanti & Pankowski 2021).

The living and widely distributed species Silis ruficollis (Fabricius, 1775) has a pronotum with a lateral margin that is less toothed and indented compared to the new fossil species described here.

Remarks. The yellow amber piece has an elongated drop shape and measures approximately 22x 11 mm. The inclusion is complete and well visible. Once trapped, the specimen struggled to get out of the sticky resin and thus created characteristic ripples (“fringes”) in the amber. A photo of this new species is included in Enrico Bonino’s forthcoming book on amber ( Bonino, 2022), expected to be published in 2022.

Figures

FIGURE 1. Silis (Silis) boninoi sp. nov. in Baltic amber. A: Holotype, dorsal view. B: Holotype, ventral view. C: Holotype, detail of prolegs. D: Holotype, detail of pronotum.