Scutellum

Bukejs, Andris & Legalov, Andrei A., 2021, Two new species of the family Rhynchitidae (Coleoptera: Curculionoidea) from Eocene Baltic amber, with key to species and assumed trophic relationships, Fossil Record 24 (1), pp. 117-127 : 120-121

Scutellum . Minute, subtriangular, poorly visible in studied specimen.

Elytra. Widely oval, elongate, convex, 2.3× as long as wide combined at anterior margin, 1.5× as long as wide combined medially, 2.0× as long as wide combined in posterior one-quarter, widest behind middle, 2.4× as long as pronotum; elytral base concave, distinctly wider than posterior pronotal margin; humeral callus weak; elytral punctation small and rather dense (punctures at lateral sides distinctly sparser), forming regular rows, distance between punctures in rows equal to 0.7–2.0× diameter of puncture, intervals slightly convex, distance between rows about 2.0–3.5× diameter of puncture.

Thorax. Prohypomera with fine and rather sparse punctation. Pre- and postcoxal parts of prosternum short, subequal in length. Epipleuron narrow, with fine punctures. Metaventrite with small punctation at lateral sides; disc convex. Metepisternum narrow, about 6.3× as long as wide medially; with fine punctation.

Legs. Rather long, slender. Procoxae conical, located in middle of prosternum; mesocoxae round; metacoxae oval, transverse, slightly shorter than abdominal ventrite 1. Femora clavate, slightly swollen in apical portion, covered with fine, sparse punctation; profemora about 3.7× as long as wide medially, metafemora about 3.9× as long as wide medially. Tibiae cylindrical, almost straight (protibiae slightly curved), with sparse and fine punctures, with fringe of dark spinulae apically, and apparently with two small apical spurs (distinctly visible on protibiae); protibial about 9× as long as wide medially, metatibia about 6× as long as wide medially. Tarsi long, slightly shorter than tibiae, metatarsus about 0.8× as long as metatibia; tarsomere 1 elongate, slightly dilated apically, tarsomere 2 subconical, elongate, tarsomere 3 bilobed, nearly as long as wide, apical tarsomere subcylindrical, elongate, slightly curved; metatarsomere 1 about 2.9× as long as maximum wide, shorter than tarsomere 5 and 1.4 times as long as tarsomere 2, 0.4× as long as tarsomeres 2– 5 combined, metatarsomere 2 about 2.1× as long as maximum wide, metatarsomere 3 about 1.1× as long as maximum wide, apical metatarsomere about 5.5× as long as maximum wide; relative length ratios of metatarsomeres 1–3, 4 subequal to 4: 3: 2: 4. Tarsal claws strongly divergent, free, simple.

Abdomen. Convex, covered with small and sparse punctation; all sutures distinct, complete and straight; ventrites 1 and 2 equal in length, ventrite 3 about 0.7× as long as ventrite 2, ventrite 4 about 0.8× as long as ventrite 3, ventrite 5 smallest, about 0.7× as long as ventrite 4, with widely rounded apical margin; relative length ratios of ventrites 1–5 equal to 6: 6: 4: 3: 2 (medially).

Note

Sex of examined specimen determined based on micro-CT results. There is no sclerotized structure resembling aedeagus inside the abdominal cavity; therefore, the specimen appears to be female.

Comparison

Baltocar sontagae sp. nov. is similar to B. groehni Riedel, 2012 but differs in the shorter rostrum; tarsomere 1 shorter than tarsomere 5 and 1.4 times as long as tarsomere 2; longer elytra and shorter body.

Key to the species of the genus Baltocar

(according to Riedel et al. (2012) and Legalov (2020a) with modifications)

1. Elytral punctation irregular. Rostrum shorter or subequal to pronotum (p. 2).

– Elytral punctation forming regular rows. Rostrum longer or subequal to pronotum (p. 3).

2. Body covered with dense setae. Rostrum slightly curved, subequal to pronotum (convexus Legalov, 2015b).

– Body without distinct pubescence. Rostrum distinctly curved, shorter than pronotum ( subnudus Riedel, 2012 ).

3. Pronotal disc coarsely punctate. Setae widened ( succinicus ( Voss, 1953)) .

– Pronotal disc transversely irregularly rugose. Setae narrow (p. 4).

4. Pronotum with slightly rounded lateral sides, about 1.1× as long as wide. Tarsomere 1 about 0.6× as long as tarsomeres 2–5 combined ( hoffeinsorum Riedel, 2012 ).

– Pronotum with subparallel lateral sides ( Fig. 2c ), 1.4× as long as wide. Tarsomere 1 about 0.4× as long as tarsomeres 2–5 combined (p. 5).

5. Rostrum long, 18.0× as long as wide medially. Tarsomere 1 slightly longer than tarsomere 5 and 1.2× as long as tarsomere 2. Elytra 1.2× times as long as maximum combined width. Body longer, 2.9 mm ( groehni Riedel, 2012 ).

– Rostrum shorter, 6.8× as long as wide medially. Tarsomere 1 shorter than tarsomere 5 and 1.4× as long as tarsomere 2. Elytra 1.5× as long as maximum combined width. Body shorter, 2.4 mm ( sontagae sp. nov.).

Remarks

The studied amber specimen possesses the combination of characters corresponding to the family Rhynchitidae : antennae not geniculate, quite long ventrites 3 and 4, narrow epipleuron, tarsal claws free at base, not extended tarsomere 1. Strongly divergent tarsal claws suggest placement in the subfamily Sayrevilleinae and tarsal claws lacking teeth assignments of the specimen to the tribe Sayrevilleini . The new species belongs to the genus Baltocar based on the short precoxal portion of the prosternum and forehead with middle furrow.

Figures

Figure 2. X-ray micro-CT renderings of Baltocar sontagae sp. nov., holotype, 6703 (MAIG), habitus: (a) dorsal view; (b) dorso-frontal view; (c) left lateral view. Scale bar = 0.5 mm.