Symbiotes borussiaeorientalis, Alekseev & Tomaszewska, 2018

Alekseev, Vitalii I. & Tomaszewska, Wioletta, 2018, New handsome fungus beetles (Coleoptera: Coccinelloidea: Anamorphidae, Endomychidae) from European amber of the Upper Eocene, Palaeontologia Electronica (6 A) 21 (1), pp. 1-23 : 10-12

Symbiotes borussiaeorientalis sp. nov.

Figure 4.1-3

zoobank.org/ DB91C913-B619-447D-930A-E816A976F371

Type material. Holotype No. 1799-2 [ CCHH], female (terminal parts of genitalia are visible; apices of elytra without small tubercles and other modifications). The beetle inclusion is preserved in a polished piece of transparent amber with an orange shade and the amber piece is embedded in polyester resin (total measurements are 11 x 9 x 4 mm). Syninclusions absent.

Type strata. Baltic amber. Eocene.

Type locality. Russia, Kaliningrad region, the Sambian (Samland) peninsula, Yantarny settlement (formerly Palmnicken) .

Etymology. The specific epithet refers to the region of the specimen’s origin and is formed after the Medieval Latin “ Borussia orientalis ” (Eastern Prussia).

Remarks. The newly described species from Baltic amber was assigned to the genus Symbiotes based of following combination of morphological characters: body form subparallel; antenna composed of 11 antennomeres; procoxal cavities open externally; pronotum with posterior margin truncate and lateral margins raised; pronotal carinae not reaching posterior margin; and tarsi 4-segmented.

Diagnosis. Symbiotes borussiaeorientalis differs from all known congeners in having coarsely and irregularly punctured elytra with distinct subsutural striae only, and scarce, poorly visible dorsal pubescence. Newly described species is 1.6 mm long, thereby smaller than most extant representatives of Symbiotes (1.7–2.4 mm), except S. gibberosus , which is 1.5–1.8 mm long. Additionally, new fossil species can be distinguished from S. duryi and S. gibberosus by having smooth (not denticulate) lateral pronotal margins; from S. latus by its less transverse pronotum (2.5 times wider than long in S. latus ), wider elytra, and dark color; from S. gibberosus by less convex body, and absence of pits at base of lateral sulci; from S. duryi , S. armatus , and S. latus by presence of subsutural stria without distinct punctation; and from S. armatus by widely rounded scutellum.

Description. Body uniformly dark brown, elongate oval, moderately convex, shiny, scarcely pubescent. Total body length 1.6 mm, width (at widest point) 0.75 mm.

Head deeply retracted in pronotum, transverse; with fine and very sparse punctation. Eyes large, prominent. Fronto-clypeal suture distinct, straight. Antennae comparatively long, extending to base of elytra; composed of 11 antennomeres, with loose club composed of three antennomeres. Antennomere length proportions follow formula: 2.5: 2.0: 1.0: 1.0: 1.0: 1.0: 1.0: 1.0: 1.5: 2.5: 3.5. Antennomeres 3–8 subequal in length and form, short and cylindrical; antennomere 9 triangular; antennomere 10 as long as wide; terminal antennomere subcylindrical, rounded apically, almost 2.0 times as long as wide. Terminal maxillary palpomere elongate, subcylindrical, tapering.

Pronotum widest at middle, strongly transverse (2.0 times wider than long); pronotal anterior and posterior margins almost straight, anterior angles obtuse, and basal angles right-angled. Lateral margins of pronotum arcuate, broad, raised, and lateral edges smooth. Median region convex, base with well-marked transverse sulcus, lateral sulci large, triangularly longitudinal, reaching anteriorly nearly one-half length of pronotum. Pronotal disc punctate: coarsely and moderately densely at sides (interspaces 1.0–2.0 times puncture diameter), more finely and sparsely near middle (interspaces 2.0–4.0 times puncture diameter).

Elytra comparatively long (3.0 times longer than pronotum), oval, decidedly wider than prothorax, attaining their greatest width within about one-third of their basal length; with explanate margins. Elytral disc coarsely and densely punctate; elytral striae absent except subsutural ones. Punctures irregular, interspaces 0.2–0.5 of diameter, denser laterally and sparser medially. Elytral epipleura pubescent. Subsutural stria distinct, broadly curved near scutellum and reaching middle of elytral base. Elytral apices conjointly rounded. Scutellum visible, transverse (about two times wider than long), widely rounded posteriorly.

Legs with procoxal cavities open externally. Metacoxae transverse, widely separated. Femur widest in middle, more than twice as wide as tibia. All tibiae simple. Tarsal formula 4-4-4. Tarsomeres simple, cylindrical; tarsomere 4 longest. Tarsal claws simple, almost 0.3 times as long as tarsomere 4.

Abdomen with five ventrites. Ventrite 1 as long as 2 and 3 combined; ventrites 2, 3, and 4 subequal in length; ventrite 5, 1.5 times longer than 4. Apex of terminal ventrite widely rounded.

Figures

FIGURE 4. Anamorphid and Endomychid from Baltic amber. 1-3, Symbiotes borussiaeorientalis sp. nov. (No. 1799-2 [CCHH], holotype), habitus in dorso-lateral (1) and ventro-lateral (2) views, and a reconstruction of the habitus in dorsal view (3). 4, Laima andreei gen. et sp. nov., a reconstruction of the habitus in dorsal view.