Stempellinella electra Giłka et Zakrzewska, 2015

Zakrzewska, Marta & Giłka, Wojciech, 2015, The Tanytarsini (Diptera: Chironomidae) in the collection of the Museum of Amber Inclusions, University of Gdańsk, Zootaxa 3946 (3), pp. 347-360 : 349-352

publication ID	https://doi.org/ 10.11646/zootaxa.3946.3.3
publication LSID	lsid:zoobank.org:pub:8D7575DB-636C-4473-91C3-A58C1E5F9E73
DOI	https://doi.org/10.5281/zenodo.5616322
persistent identifier	https://treatment.plazi.org/id/03CD3E7A-7115-A717-FF60-AA9FD1A9F76F
treatment provided by	Plazi
scientific name	Stempellinella electra Giłka et Zakrzewska
status	sp. nov.

Treatment

Stempellinella electra Giłka et Zakrzewska View in CoL , 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 View FIGURE 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 View FIGURE 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 View FIGURE 3 D, E). Length of palpomeres 2–5 (in µm): c. 30, 64, 84, 133. Clypeals present, but cannot be counted.

Thorax ( Fig. 3 View FIGURE 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 View FIGURE 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 View TABLE 1 .

Hypopygium ( Fig. 4 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 3 C), the wing vein R4+5 ending opposite to M3+4 ( Fig. 3 View FIGURE 3 F), the broadened superior volsella, and the gonostylus shorter than the gonocoxite ( Fig. 4 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 3 D, E) than that plesiomorphic state known from S. ivanovae (only flagellomeres 12 and 13 fused in part; Zakrzewska & Giłka 2014: fig. 3C).