Stempellinella electra Gilka et Zakrzewska, sp. nov.
Creators: name: Zakrzewska, Marta
name: Giłka, Wojciech
Publisher: name: Zenodo
Year: 2015
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Chironomidae
Stempellinella
Stempellinella electra

description: Stempellinella electra Giłka et Zakrzewska, sp. nov.
Type material. Holotype. Adult male, complete specimen with large mite attached under right wing, preserved in 14 x 11 x 2 mm piece of amber (Eocene, ~45–40 Ma, Baltic amber, Gulf of Gdańsk; MAI-4295a; Fig. 3 A); animal syninclusions: Acari (2 ind., MAI-4295a), Mycetophilidae (1 ind., MAI-4295b), Aphidoidea (1 ind., MAI-4295).
Derivatio nominis. Adjective in feminine form derived from the Latin noun ‘ electrum ’, amber.
Diagnosis. Antennal flagellum composed of 13 segments, flagellomeres 11–13 fused in part. Anal point with slender distal section and strong crests. Superior volsella elongated, with round apex, bearing 2 setae. Stem of median volsella club-shaped, with wide pectinate and foliate lamellae. Inferior volsella arcuate, tapering to pointed apex armed with 2 stout setae.
Description. Adult male (n = 1)
Total length c. 1.5 mm; wing length c. 890 µm.
Head (Fig. 3 C–E). Eyes bare, small, ovoid, broadly separated. Frontal tubercles conical, c. 10 µm long. Antennal flagellum composed of 13 segments of which 11 are well discernible, flagellomeres 11–13 fused in part, AR 0.76 (when flagellum measured as 11-segmented), AR 0.62 (as 12-segmented), AR 0.50 (as 13-segmented); plume fully developed (Fig. 3 D, E). Length of palpomeres 2–5 (in µm): c. 30, 64, 84, 133. Clypeals present, but cannot be counted.
Thorax (Fig. 3 B). Ac at least 11, Dc at least 7-8 on each side, Pa 1 on each side, Scts at least 4.
Wing (Fig. 3 F). Slender, with anal lobe weak, broadest at 2/3 length; width: 285 µm, length/width ratio: 3.12. Sc ending slightly distal of FCu, R2+3 fading, poorly visible. RM slightly oblique relative to R. FCu placed well distally of RM; VR Cu 1.38. Veins ending as follows (in order from base to tip): An, Sc, Cu1, R1, R4+5 and M3+4, M1+2. Wing covered with dense macrotrichia in distal half at least.
Legs. Tibial apices including combs of mid and hind legs weakly visible. Spurs not observed on forelegs. Only one spur visible on mid leg (c. 20 µm long) and hind leg (c. 28 µm long). Sensilla chaetica on ta1 of p2 not observed. Lengths of leg segments and leg ratios in Table 1.
Hypopygium (Fig. 4 A–D). Gonostylus c. 50 Μm long, shorter than gonocoxite, broadest at mid-length, tapering to blunt apex armed with strong apical setae. Anal tergite subtriangular, with several median setae and at least 7 posterolateral setae on each side of anal point (poorly visible on photographs). Anal point broad at base, distinctly narrowed distally, with slender distal section and strong crests tapering towards anal point tip. Superior volsella elongated, with broadened round apex, bearing 2 setae on median margin. Digitus absent. Stem of median volsella club-shaped, slightly broadened apically, c. 20 µm long, with several setiform and 4–5 wide pectinate and foliate lamellae (Fig. 4 A, B, D). Inferior volsella reaching 2/3 length of gonostylus at most, somewhat arcuate, tapering to pointed posteromedially directed apex, with several strong setae including 2 stout setae on apex (Fig. 4 A–C).
Remarks. Stempellinella electra is the third fossil species of the genus found in Eocene amber, along with S. bicorna Seredszus et Wichard, 2007 and S. ivanovae Giłka et Zakrzewska, 2014 (Seredszus & Wichard 2007, Zakrzewska & Giłka 2014). The new species fits well the emended generic diagnosis for Stempellinella Brundin, 1947 (Ekrem 2007) —the adult male has bare ovoid and broadly separated eyes (Fig. 3 C), the wing vein R4+5 ending opposite to M3+4 (Fig. 3 F), the broadened superior volsella, and the gonostylus shorter than the gonocoxite (Fig. 4). Significant differences in the hypopygium structure have been observed between the three fossil Stempellinella species. S. electra is distinct in having a long anal point, broad at base and narrowed distally (in contrast to the short anal point in S. bicorna) bearing strong anal point crests (Fig. 4 B, C)—not observed in the two fossil relatives, but resembling those known from several extant species (cf. Ekrem 2007). The best diagnostic characters for S. electra is the superior volsella elongated and broadened apically, the inferior volsella arcuate and pointed, and the median volsella bearing several setiform and 4–5 wide pectinate and foliate lamellae (Fig. 4 A, B, D)—the combination of shapes not recorded neither in fossil or extant Stempellinella (the pectinate lamellae are known only from S. reissi Casas et Vilchez-Quero, 1991).
It is worth noting that we observed a tendency to formation of a fully-segmented antennal flagellum in Stempellinella electra, similar to that known from S. ivanovae. However, when comparing this character in these two species, the higher number of incompletely fused flagellomeres may indicate more advanced state in S. electra (flagellomeres 11–13 fused in part, Fig. 3 D, E) than that plesiomorphic state known from S. ivanovae (only flagellomeres 12 and 13 fused in part; Zakrzewska & Giłka 2014: fig. 3C).
description: Published as part of Zakrzewska, Marta & Giłka, Wojciech, 2015, The Tanytarsini (Diptera: Chironomidae) in the collection of the Museum of Amber Inclusions, University of Gdańsk, pp. 347-360 in Zootaxa 3946 (3) on pages 349-352, DOI: 10.11646/zootaxa.3946.3.3, http://zenodo.org/record/245390