Tanytarsus glaesarius 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
Tanytarsus
Tanytarsus glaesarius

description: Tanytarsus glaesarius Giłka et Zakrzewska, sp. nov.
Type material. Holotype. Adult male (tarsi of left fore and hind leg missing, tarsi of mid legs broken and separated) preserved in 21 x 13 x 1 mm piece of amber (Eocene, ~45–40 Ma, Baltic amber, Gulf of Gdańsk; MAI- 415a; Fig. 5 A); animal syninclusions: Ceratopogonidae, Formicidae, Mordellidae, Thysanoptera, Psocoptera (all as single ind., MAI-415).
Derivatio nominis. Adjective derived from the Latin noun ‘ glaesum ’, amber.
Diagnosis. Frontal tubercles stout, cylindrical. Antenna with flagellomeres 10–11 fused in part and 12–13 completely fused. Wing vein FCu placed far distally of RM (VR Cu 1.52). Anal point wide at base, distinctly narrowed subapically, tapering to pointed apex. Superior volsella with 2 setae on apex. Digitus long, extending beyond superior volsella, curved, with blunt apex. Stem of median volsella bulbous, with slender foliate lamellae.
Description. Adult male (n = 1)
Total length c. 1.2 mm; wing length c. 820 Μm.
Head (Fig. 5 C–E). Eyes bare, reniform, with dorsomedian extensions (Fig. 5 C). Frontal tubercles stout, cylindrical with blunt apices, c.15-20 Μm long (Fig. 5 D). Antennal flagellum composed of 11 segments of which 10 are well discernible, flagellomeres 10–11 fused in part (borders between remaining flagellomeres not visible, but distribution of setal tubercles indicates 13 segments), AR 0.82 (when flagellum measured as 10-segmented), AR 0.65 (as 11-segmented); plume fully developed (setae separated, but setal tubercles well developed) (Fig. 5 E). Length of palpomeres 2–5 (Μm): c. 30, 60, 76, 129. At least 15 clypeals.
Thorax. Ac and Dc not visible (thorax damaged in dorsal part), Pa 3 on each side, Scts 6 at least.
Wing (Fig. 5 F). Slender, with anal lobe weak, broadest at 2/3 length, width: 260 Μm, length/width ratio 3.15. FCu placed far distally of RM; VR Cu 1.52. Veins ending as in most extant Tanytarsus (from base to tip): An, Sc, Cu1, R1, R2+3, M3+4, R4+5, M1+2; distances between ends of R1–R2+3 and R2+3–R4+5 unequal (VR C c. 2.15). Almost whole wing (except base) covered with dense macrotrichia.
Legs. Tibia of fore leg without spur. Tibial combs of mid and hind legs separated, fan-shaped, teeth up to 16 Μm long; each comb with slender spur, 26 Μm long (mid leg) and 20–32 Μm long (hind leg). Sensilla chaetica on ta1 of p2 not observed. Lengths of leg segments and leg ratios in Table 2.
Hypopygium (Fig. 6 A–E). Gonostylus stout, slightly arcuate, c. 50 Μm (as long as gonocoxite), with sparse setae placed on median margin in distal half. At least 2-3 tubercles bearing posterolateral setae on each side of anal point. Anal point wide at base, distinctly narrowed subapically, tapering to pointed apex; spinulae or crests unobservable from ventral side. Superior volsella (visible only in distal part) with 2 setae on apex; digitus long, extending beyond superior volsella, curved, with blunt apex (Fig. 6 D). Stem of median volsella bulbous, c. 15 Μm long, with 3 slender foliate lamellae (Fig. 6 E). Inferior volsella reaching half length of gonostylus, stout, with slightly swollen apical half posteromedially directed, armed with several curved setae on apex and strong setiform microtrichia on posterolateral margin (Fig. 6 A–C).
Remarks. A set of characters given in the diagnosis and description (except the number of antennal flagellomeres, see remarks below), indicate that the new species belongs to the genus Tanytarsus. Several significant characters, i.e. the shape of the hypopygial superior volsella (with 2 setae on apex), the digitus (long, extending far beyond superior volsella), and the median volsella (with stout bulbous stem and slender foliate lamellae) are known from species of different systematic groups, e.g. the eminulus- mendax - or chinyensis group (cf. Reiss & Fittkau 1971, Ekrem 2003, Giłka & Paasivirta 2009). However, these characters form a combination unknown from any extant or fossil Tanytarsus, thus a group membership of Tanytarsus glaesarius remains open. Tanytarsus glaesarius is the first Eocene species of this genus known from the adult male having the antenna with the reduced number of flagellomeres (Fig. 5 E). This character is similar to that discussed above (see remarks on Stempellinella electra), but we propose to weigh it differently on a background of all known Tanytarsus, including extant species of this genus (males with 13 flagellomeres). Since we have not observed other characters that might suggest non-typical structure (e.g. deformations, asymmetry, brachyptery or other associated features known from non-flying chironomids; cf. Giłka 2011b, Giłka et al. 2013a), we assume that the reduced number of flagellomeres observed in T. glaesarius should be treated as a species-specific feature rather than a character which might be considered in the context of phylogenetic trends.
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 353-356, DOI: 10.11646/zootaxa.3946.3.3, http://zenodo.org/record/245390