Tanytarsus colombiensis, Dantas & Amat & Hamada & Giłka, 2022

Dantas, Galileu P. S., Amat, Eduardo, Hamada, Neusa & Giłka, Wojciech, 2022, Towards the systematics and diversity of Neotropical Tanytarsus van der Wulp (Diptera: Chironomidae): news from Colombia, Zootaxa 5129 (4), pp. 505-529 : 508-510

Tanytarsus colombiensis sp. nov.

LSID: urn:lsid:zoobank.org:act:160B07E4-B418-4690-8F64-A21DC8D90AD7

( Fig. 2A–G )

Type material. Holotype, adult male: COLOMBIA, Meta Department, Puerto Lopez , 04º08’11’’N 72º52’53’’W, 206 m a.s.l., 01–03 January 2021, Malaise trap, G.P.S. Dantas, S.M. R. Hernández (CETdeA).

Derivatio nominis. In reference to the country— terra typica of the species.

Diagnosis. Frontal tubercles small. Anal tergite bands T-shaped. Anal point deeply forked and strongly curved downwards, apex of each branch notched and slightly curved outwards. Median volsella with setiform and branched lamellae.

Description. Adult male (n = 1).

Body size and proportions. Total length 2.08 mm. Wing length 1.15 mm. Total length/wing length ratio 1.81. Wing length/length of profemur ratio 1.97.

Colouration. Eyes black. Antenna brown, head capsule and palp light brown. Scutal vittae and postnotum light brown. Ground colour of thorax, scutellum, and haltere yellowish. Foreleg: all segments light brown. Mid and hind legs: femora yellowish, tibiae and tarsomeres light brown. Wing membrane with pale brownish undertone. Abdomen light yellowish, hypopygium slightly darker.

Head. Eyes bare, with well-developed dorsomedian extensions. Antenna with 13 flagellomeres; ultimate flagellomere 331 μm long; AR 0.85. Frontal tubercles small, 8 μm long. Tentorium 110 μm long. Temporal setae 7 on each side. Clypeus with 10 setae. Lengths of palpomeres 1–5 (in μm): 28, 32, 80, 90, 175; sensilla clavata not observed on third palpomere.

Thorax. Ac 16, restricted to anterior region of scutum; Dc 7 on each side, uniserial; Pa 1 on each side; Scts 4. Scutum projected and rounded anteriorly, overreaching antepronotum.

Wing. Typical of the genus. Almost all veins (except subcosta) and entire membrane posterior to radial veins area (except base of m cell) covered with macrotrichia. Brachiolum with 1 seta. VRCu 1.26. WW 0.27.

Legs. Foreleg tibia with straight lanceolate spur 13 μm long. Tibial combs of mid and hind legs separated; spurs of mid leg unequal: one bent, 15 μm long, second straight and shorter, 11 μm long; spurs of hind leg unequal: one bent 24 μm long, second straight and shorter, 18 μm long. Basitarsus of mid leg with 4 sensilla chaetica. Lengths and proportions of legs as in Table 1 .

Hypopygium. Tergite IX covered with dense short microtrichia, except for small median field free of microtrichia at base, dorsal/median setae absent, 4 long setae on each side of anal point; lateral teeth not observed; anal tergite bands T-shaped, ending well anterior to anal point base ( Fig. 2A, C ). Anal point 70 μm long, deeply forked and strongly curved downwards, apex of each branch notched and slightly curved outwards ( Fig. 2A–E ). Superior volsella 32 μm long, with posteromedian corner pointed; 4 setae on dorsal surface and 2 ventral setae placed close to median margin; digitus 15 μm long, finger-like, with basal part slightly extending beyond posterior margin of superior volsella but with apex not reaching its median margin ( Fig. 2A–C ). Stem of median volsella 14 μm long, medially directed, with setiform and branched lamellae, as shown in Fig. 2F, G . Inferior volsella ~65 μm long, covered with microtrichia, evenly curved, posteriorly directed. Phallapodeme slightly sinuous, ~95 μm long; transverse sternapodeme ~40 μm long; oral projections slight. Gonocoxite 100 μm long. Gonostylus 75 μm long, straight, parallel-sided, with apex round. HR 1.33. HV 2.77.

Distribution and ecological notes. The species is known only from the type locality in central Colombia, where the vegetation corresponds to mosaics of savannas, mainland forests and flooded forests ( Fig. 1A–C ). The holotype specimen was collected over a small stream about 1 meter wide and with negligible current, which is bordered by a relatively well-preserved gallery forest ( Fig. 1B ). It is worth noting that the point where the trap was placed, was located about 10 meters upstream of a dammed area, which formed a small pond ( Fig. 1C ).

Discussion. A tendency to split, i.e. forming a bi- or trifid hypopygial anal point is a rare character within Tanytarsus . In some species the anal point is divided into lobes, with the split restricted to apical part, usually with median protrusion or extension between. The anal point can be also deeply forked, with a distinct bifurcation beginning near its base. We treat these two character states or structure types as clearly different. The first one is typical mainly of species originally included in Caladomyia [= Tanytarsus ortoni species group in the current definition ( Lin et al. 2018)], while the second is known from males of only one species— Tanytarsus caipira described from Brazil ( Trivinho-Strixino & Strixino 2007). Yet another shape of a split anal point is shown in Tanytarsus richardsi Glover, 1973 from Australia, in which the bifurcation is restricted to distal portion, and the anal point is Y-shaped or slingshot-shaped ( Glover 1973). We define this structure as unique, and presume a need of inclusion of T. richardsi in a separate species group that is not, however, an aim of this study.

To a group of species displaying the first aforementioned structure type, apart from the species known as members of the ortoni group, we preliminarily include also Tanytarsus bifurcus Freeman, 1958 described from West Africa ( Burkina Faso) and Tanytarsus biwatrifurcus Sasa et Kawai, 1987 from Japan ( Freeman 1958, Sasa & Kawai 1987). The two species were placed in Tanytarsus , and have not been previously considered the members of Caladomyia or the ortoni group, probably due to their great distance from region of the highest diversity (Neotropics). In fact, a set of hypopygium structures, including the anal point in the two species, fits the concept of the ortoni group. If so, the group has a much wider range than that known to date, covering the South and Central America, the tropical/subtropical ecozone of North America, Africa and East Asia. Such the distribution pattern, including the Palaearctic region, support a concept by Zakrzewska and Giłka (2013) based on the fossil record and indicating a broad distribution of the ortoni group in the past (Eocene Baltic amber, ~40 Mya).

Tanytarsus colombiensis is here defined as a closest known relative of T. caipira . In males of the two species the anal point is deeply forked, the superior volsella is bare, without a field of microtrichia on its dorsal surface, pyriform, with a hook-like apex directed anteromedially, the digitus is short, with apex round, hidden under the superior volsella, and the stem of the median volsella is more or less as short as the digitus. Consequently, we here propose the caipira group for the two species. The character set best delimiting the males of both species includes the anal point branches notched apically and the T-shaped anal tergite bands in T. colombiensis ( Fig. 2 ) vs. the branches pointed and the anal tergite bands of V-type broadly separated in T. caipira ( Trivinho-Strixino & Strixino 2007; figs 1, 2).

Figures

FIGURE 1. Sites of sampling the material in Colombia (Meta Department, Puerto Lopez).

FIGURE 2. Tanytarsus colombiensis sp. nov., male. A, B: hypopygium in dorsal (A) and ventral aspect (B); C: arrangement of anal tergite, anal point, superior volsella and digitus; D, E: anal point in dorsal (D) and lateral view (E); F, G: median volsella photographed (F) and drawn (G); (D–G magnified ca. 3 times relative to A and B).