Tanytarsus gnomon, 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 : 513-515

Tanytarsus gnomon sp. nov.

LSID: urn:lsid:zoobank.org:act:8FF8DF78-6BA1-4661-B38C-560195B62C38

( Fig. 4A–F )

Type material. Holotype: male, COLOMBIA, Huila Departament, Yaguará, Condominio Santa Helena , 2°39’40.86”N 75°31’0.03”W, 570 m a.s.l., 06 March 2018, sweep net, G.P.S. Dantas, S.M. R. Hernández, E.C.G. Amat (CETdeA).

Derivatio nominis. In reference to the shape of the anal point with its posterior bar, resembling a sundial clock hand (Lat. gnomon ). Noun in apposition.

Diagnosis. Frontal tubercles small. Tergite IX covered with dense short microtrichia except for two bare fields lateral to anal point base. Anal point with well-developed anal crests extending towards tergite IX and flanking a small cone-shaped anterior bar, posterior bar slender, evenly curved upwards, with apex slightly enlarged and split. Superior volsella with posteromedian corner strongly narrowed, in shape of finger-like projection, with apex swollen and medially directed. Digitus subtriangular, pointed, reaching half length of superior volsella. Median volsella with 1 foliate and 3 setiform lamellae.

Description. Adult male (n = 1).

Body size and proportions. Total length 2.39 mm. Wing length 1.25 mm. Total length/wing length ratio 1.90. Wing length/length of profemur ratio 1.71.

Coloration. Eyes black. Antenna light brown. Head capsule and thorax yellow to light brown. Legs yellowish to light brown. Wing veins yellow, membrane pale. Abdomen yellow.

Head. Eyes bare, with well-developed dorsomedian extensions. Antenna with 13 flagellomeres; ultimate flagellomere 446 μm long; AR 1.01. Frontal tubercles small, 4 μm long. Tentorium 105 μm long. Temporal setae 9 on each side. Clypeus with 11 setae. Lengths of palpomeres 1–5 (in μm): 24, 28, 78, 90, 160; third palpomere with 2 sensilla clavata subapically, 12 μm long.

Thorax. Ac 16, restricted to anterior region of scutum; Dc 5 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 and an cells) covered with macrotrichia. Brachiolum with 1 seta. VRCu 1.15. WW 0.28.

Legs. Foreleg tibia with straight lanceolate spur 15 μm long. Tibial combs of mid and hind legs separated; spurs of mid leg unequal: one bent, 24 μm long, second straight, 12 μm long; spurs of hind leg unequal: one bent 28 μm long, second straight 27 μm long. Basitarsus of mid leg without sensilla chaetica. Lengths and proportions of legs as in Table 3.

Hypopygium. Tergite IX covered with dense short microtrichia except for two bare fields lateral to anal point base, with 5 median setae placed between anal tergite bands and 4 setae on each side of anal point; lateral teeth present, minute; anal tergite bands V-shaped, widely separated, ending anterior to anal point base ( Fig. 4A ). Anal point 55 μm long, somewhat lanceolate, with elongated and rounded tip, bearing well-developed, 22 µm long anal crests extending towards tergite IX and flanking a small, 8 μm long, cone-shaped anterior bar, posterior bar slender, evenly curved upwards, with apex slightly enlarged and split ( Fig. 4A, C ). Superior volsella 44 μm long, with posteromedian corner strongly narrowed, in shape of finger-like projection swollen apically and directed medially; with 5 setae on dorsal surface and 3 ventral setae close to median margin (at least 2 setae placed on prominent tubercles), field of microtrichia on dorsal surface absent; digitus 11 μm long, subtriangular, pointed, reaching half length of superior volsella ( Fig. 4A–D ). Stem of median volsella 11 μm long, with 1 foliate and 3 setiform lamellae ( Fig. 4B, E, F ). Inferior volsella ~60 μm long, covered with microtrichia, with distal half slightly curved, swollen and posteromedially directed. Phallapodeme sinuous, ~65 μm long; transverse sternapodeme ~50 μm long, with strong oral projections. Gonocoxite 95 μm long. Gonostylus 85 μm long, almost straight, evenly tapering towards pointed apex. HR 1.14. HV 2.81.

Distribution and ecological notes. This species is known only from the type locality in the Huila department, at the inter-Andean valley of Magdalena River basin, reaching the 570 m elevation. Next to the type locality are some small artificial lakes and a first-order stream. However, attempts to collect the immature stages of the new species in these environments were unsuccessful.

Discussion. Sanseverino (2006) discussed relationships between Tanytarsus curvicristatus and species of the Tanytarsus signatus group, as well as those of former Caladomyia and Virgatanytarsus —the names evidenced as synonyms of Tanytarsus ( Lin et al. 2018) , thus validating a previously postulated concept of Cranston (2000) for Virgatanytarsus . The Sanseverino’s analysis was based on morphology of male hypopygium, mainly the anal point and its bars—the structures present in all the taxa analysed. In the dissertation, relations between T. curvicristatus , T. signatus (Holarctic) and T. liepae ( Australia) were defined as close and possibly closer to each other than to species of the former Caladomyia and Virgatanytarsus . Due to a peculiar structure of the anal point in T. curvicristatus , a new species group for this species was also suggested. A close species described later, T. pseudocurvicristatus , supported this concept ( Trivinho-Strixino et al. 2015). Further, molecular analyses indicated T. signatus as a lineage genetically divergent from that of T. curvicristatus , while the latter species and its morphologically close relatives, including T. pseudocurvicristatus , again were suggested to be placed in a separate species group ( Lin et al. 2018). Another two species, presented here as new, made it possible to formulate a diagnosis based on characters found in all four species, and to establish the previously expected Tanytarsus curvicristatus species group. These characters are the shape and arrangement of the anal point crests, bars, the lack of the spinulae typical of most Tanytarsus , as well as the shape of the superior volsella and digitus (see the group diagnosis). The anal point bar(s) shape/ arrangement seems to be crucial in phylogeny analyses based on morphology of Tanytarsus . These structures have recently been studied in both extant and fossil species ( Trivinho-Strixino 2012, Zakrzewska & Giłka 2013, Dantas & Giłka 2017), although they are found in only a few species groups of the genus.

Figures

FIGURE 4. Tanytarsus gnomon sp. nov., male. A, B: hypopygium in dorsal (A) and ventral aspect (B); C: arrangement of anal point, superior volsella and digitus; D: superior volsella and digitus; E, F: median volsella drawn (E) and photographed (F); (C–F magnified ca. 2–3 times relative to A and B).