Tanytarsus ramus, 2020

TANYTARSUS RAMUS GIŁKA & ZAKRZEWSKA View in CoL SP. NOV.

( FIGS 4A–F, 5A–F, 11D)

LSID: urn:lsid:zoobank.org:act:D8802738-369F-4D19-823F-379C31FFA80B

Type material

Holotype, inventory no. BSIP Tad-521: adult male (tarsi of left foreleg and of both mid- and hindlegs missing; Fig. 4A, B) in a 7 mm × 5 mm × 2.5 mm piece of amber preserved in a cubicoid plastic mass (early Eocene , ~54 Mya, Tadkeshwar mine, Gujarat state, India; IR spectrum no. 14257 IAA, Fig. 11D).

Etymology

From Latin ramus , branch or twig, refering to the frail, simply branched median volsellae. Noun in apposition.

Diagnosis

Wing vein Sc extending well beyond RM; FCu placed well distal to RM; distance between ends of R

1

–R

2 + 3

and R 2 + 3 –R 4 + 5 unequal, VR C ~5. Tibial combs and spurs stout, combs fan shaped, only one comb with spur on mid-leg, each comb with spur on hindleg. Anal tergite with three spinulae in a row, placed in pit surrounded by crest-like ridges. Anal point slender, long, reaching apex of inferior volsella. Superior volsella pipe shaped. Stem of median volsella twig shaped, branched into two simple, slender lamellae. Inferior volsella parallel sided.

Description

Adult male (N = 1). Total length ~ 2.1 mm; wing length ~840 μm.

Head ( Fig. 4B): Eyes bare, slightly produced in dorsomedian position. Frontal tubercles not observed. Antenna with 13 flagellomeres, AR unmeasurable, plume fully developed. Length of palpomeres 2–5 (in micrometres): ~25, 105, 105 and 169. At least 12 strong clypeals.

Thorax: Dc at least nine, Pa at least one, other thoracic setae unobservable.

Wing ( Fig. 4C): Anal lobe relatively well developed, broadest at two-thirds of length, width 265 μm, length/ width ratio 3.17. Sc extending well beyond RM. RM slightly oblique relative to M and R. R 1 and R 2 + 3 arcuate in distal section. FCu placed well distal to RM; VR Cu 1.35. Veins ending as follows (in order from base to tip): An, Sc, Cu 1, R 1, R + 2 3, M + 3 4, R + 4 5, M + 1 2; distance between ends of R 1 –R 2 + 3 and R 2 + 3 –R 4 + 5 unequal; VR C ~5. Wing membrane covered with macrotrichia in distal half.

Legs: Tibia of foreleg with stout spur ~25 μm long. Tibial combs of mid leg fan shaped, teeth ≤ 25 μm long, only one comb bearing slender spur ~55 μm long ( Fig. 4D, E); combs of hindleg broadly separated, fan shaped; one comb broad, with teeth ≤ 25 μm long, bearing spur ~50 μm long; second comb slender, teeth ≤ 30 μm long, bearing spur ~60 μm long ( Fig. 4F). For the leg segment lengths and leg ratios, see Table 3.

Hypopygium ( Fig. 5A–F): Gonostylus slightly longer than gonocoxite, ~85 μm long, tapering towards pointed apex. Anal tergite semicircular, bearing three spinulae arranged in a row, placed in rounded, longitudinal pit, its crest-like ridges tapering towards base of anal point; several setae on each side. Anal point long, reaching apex of inferior volsella, slender, parallel sided with blunt tip; severalstrongposterolateralsetaeoneachside( Fig.5A,B). Superior volsella pipe shaped, with oval basal part, distinctly narrowed at mid-length, distal part elongate with apex blunt; several short setae at median margin of basal part ( Fig. 5B, D). Digitus not observed. Stem of median volsella ~20 μm long, posteromedially directed, twig shaped, branched into two simple, slender lamellae ( Fig. 5C, E, F). Inferior volsella reaching half the length of the gonostylus, nearly parallel sided, with distal half armed, bearing numerous stout setae.

Remarks

Tanytarsus ramus differs from all known species of the genus by a set of distinct characters as follows: the VR C ratio is nearly five ( Fig. 4C), the anal tergite has a couple of spinulae placed in a row in a large pit, and the anal point is slender and extraordinarily long ( Fig. 5A, B); the pipe shaped superior volsella should be considered a key feature ( Fig. 5B, D), whereas the digitus, typical of Tanytarsus , is not observed (probably absent). The most peculiar structure diagnostic of T. ramus is the hypopygial median volsella ( Fig. 5E, F) of a shape perceived as a plesiomorphy (see Discussion: Evolution of the diagnostic structures).