Tanytarsus protogregarius Gilka et Zakrzewska, sp. nov.

Tanytarsus protogregarius Giłka et Zakrzewska, sp. nov.

Type material. Holotype. Adult male (tarsi of hind legs broken and separated) preserved in 15 x 13 x 5 mm piece of amber (Eocene, ~45–40 Ma, Baltic amber, Gulf of Gdańsk; MAI-4325a; Fig. 7 A); animal syninclusion: Sciaridae (1 ind., MAI-4325). Paratypes. Two adult males (tarsi of all legs broken and separated and/or missing, wings poorly preserved), as syninclusions, slightly compressed, preserved in 16 x 18 x 4 mm piece of clarified amber (MAI-4352, same data as holotype; Fig. 7 B).

Derivatio nominis. Combination of two words: ‘ protoplastus ’ and ‘ gregarius ’. The species is the oldest known representative of the Tanytarsus gregarius species group.

Diagnosis. Femur of mid leg longer than femur of hind leg. Gonostylus with subapical tooth-like process. Anal point slender, tapering to blunt apex, bearing spinulae arranged in row. Superior volsella posteriorly directed, with nipple-like extension on apex and 4 strong medially directed setae on median margin. Digitus not observed. Stem of median volsella long, straight, with 5–6 slender foliate lamellae.

Description. Adult male (n = 1–3)

Total length 2.6–3.1 mm; wing length 1475–1575 Μm.

Head (Fig. 7 D, E). Eyes bare, with well developed dorsomedian extensions. Frontal tubercles not observed. Antenna with 13 well discernible flagellomeres, AR 0.92–0.97, plume fully developed (Fig. 7 E). Length of palpomeres 2–5 (Μm): 40–48, 113–137, 115–125, 149–185. Clypeals present but poorly visible (at least 4–6 in paratype specimens).

Thorax. Ac at least 12, Dc 13 on each side, Pa 3 on each side, Scts 12–13.

Wing (Fig. 7 F, G). Ellipse-shaped, with anal lobe weak, broadest at 2/3 length, width: 385–395 Μm, length/ width ratio 3.83–3.98. FCu placed well distally of RM; VR Cu 1.33. 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 1.35). Almost whole wing (except base) covered with dense macrotrichia.

Legs. Tibia of fore leg with single, 28–30 Μm long spur (a vestigial comb composed of 2–3 teeth, observed on one leg of paratype specimen is recognized as artefact). Tibial combs of mid and hind legs separated, fan-shaped, teeth up to 20 Μm long (mid leg) and c. 20–24 Μm long (hind leg); each comb with slender spur, up to 30 Μm long (mid leg) and 36–48 Μm long (hind leg). Sensilla chaetica on ta1 of p2 not observed. Lengths of leg segments and leg ratios in Table 3.

Hypopygium (Fig. 8 A–F). Gonostylus stout, slightly curved at mid length, c. 95–115 Μm, longer than gonocoxite, bearing several setae placed at median margin of distal half, with subapical anteromedially directed tooth-like process. Median setae on anal tergite not observed, at least 3 posterolateral setae on each side of anal point. Anal point slender, tapering to blunt apex, bearing at least 3 spinulae arranged in row, crests tapering towards anal point apex. Superior volsella posteriorly directed, oval, slightly elongated, with nipple-like extension on apex and 4 strong medially directed setae placed on distinct protuberances on median margin (Fig. 8 D). Digitus not observed. Stem of median volsella c. 25 Μm long, straight, bearing 5–6 slender foliate lamellae (Fig. 8 E, F). Inferior volsella reaching 1/3 length of gonostylus at most, club-shaped, with posteromedially turned head-like apical part, armed with several stout curved setae.

Remarks. Tanytarsus protogregarius is here proposed to be included in the gregarius species group due to a distinct similarity to the extant species— Tanytarsus gregarius Kieffer, 1909. Both the species are similar in the shape of the anal point and the superior volsella that is posteriorly directed and armed with nipple-like apical extension (cf. Fig. 8 and Reiss & Fittkau 1971, fig. 26). The best characters separating the new species from other members of the group is the subapical tooth-like process of the gonostylus and the presence of four strong medially directed setae on median margin of the superior volsella (three strong setae are known from extant species). Moreover, in the adult male of T. protogregarius we observed interesting proportions of leg segments. In all examined individuals femora of mid legs are longer than those of hind legs (Table 3). Similar proportions we found in other fossil species— Tanytarsus congregabilis Giłka et Zakrzewska, 2013 of the lugens group. It may indicate close relations between the two groups, which were previously proposed also to be treated as one—the concept based on adult male morphological characters of extant species (Giłka 2000). The latter character discussed, however, is not known from any extant European species of these two groups [T. gregarius, T. aberrans Lindeberg, 1970, T. inaequalis Goetghebuer, 1921, and T. lugens (Kieffer, 1916), T. bathophilus Kieffer, 1911, T. latiforceps Edwards, 1941, T. trux Giłka et Paasivirta, 2007; all examined], in which femora of mid legs are typically shorter than those of hind legs.