Tanytarsus limneticus Sublette, 1964

Sanseverino, Angela M., Trivinho-Strixino, Susana & Nessimian, Jorge L., 2010, Taxonomic status of Nimbocera Reiss, 1972, a junior synonym of Tanytarsus van der Wulp, 1874 (Diptera: Chironomidae), Zootaxa 2359, pp. 43-57 : 49-53

Tanytarsus limneticus Sublette, 1964

( Figs 16–25 )

Nimbocera pinderi ( Steiner & Hulbert, 1982) ; 4th instar larvae. Synonymised by Epler (1992).

Type material ( USA). Paratypes: 1 adult male, Louisiana, Natchitoches, U.S. Fish Hatchery, 20.IX.1958, leg. R. F. Tyler (Collection of J. E. Sublette); 1 adult male as previous except 12.IX.1958, specimen remounted in Euparal, leg. J. E. Sublette (Collection of J. E. Sublette).

Additional material examined: Nimbocera pinderi ( Steiner & Hulbert, 1982) : 1 adult male, USA, Florida, Boca Grande, a lab pond, 27.XII.1982, R. Rutter ( ZMBN); 1 adult male plus 1 pupal exuviae as previous, 2 pharate males as previous.

Diagnosis. Male Imago: AR about 1.37; large frontal tubercles; dorsocentrals in one row, close to scutellum in a group of 2–4 setae; high number of acrostichals and scutellars; 2–3 prealars; M and Sc veins with setae; tergite IX without microtrichia-free areas; anal tergal bands separate, curved; anal point with pair of well developed anal crests; spines placed irregularly between anal crests, 2 shorter setae are present anteriorly between crests; superior volsella with field of microtrichia on anterolateral margin, posteromedian corner projecting; digitus pointed, triangular to somewhat cone-like, not extending or extending a little beyond margin of superior volsella; median volsella with foliate lamellae.

Pupa: Frontal setae short, cephalic tubercles weakly developed; prealar somewhat rounded to quadrate and inwardly folded; thoracic horn thin and with spinules; three precorneals not in triangular pattern, placed on an tubercle; tergite II with median homogeneous shagreen; T III with pair of long bands of longer spines placed on posterior half of tergite and lateral fields of fine shagreen, bands anteriorly straight, posteriorly curved outward; T IV with bracket-shaped pair of long bands of spines, anterior part with thin short spines directed to caudal and median, posterior part with longer spines directed to oral; T V–VI with anterior pair of rounded spine patches; T VIII with fine anterolateral shagreen; T IX with anterior shagreen; posterolateral comb of segment VIII quite broad; abdominal segment I with 2 dorsal long taeniae and without lateral seta, segment II–VII with 3 lateral setae, segment VIII with 3 lateral taeniae, 1 dorsal seta and 1 ventral taenia.

Larva: Antennal pedestal without spur, segment 2 of antenna with narrow, not sclerotized ring near base; AR 1.66; Lauterborn organs small, situated on apex of long and slim pedicels, pedicels annulated for about 4/ 5 of their length; mentum with pale, pentamerous median tooth and 5 pairs of brown lateral teeth; mandible with dorsal pale tooth, apical tooth and 3 inner teeth brown to dark brown.

Description. Male Imago (n = 4)

Head. AR 1.33–1.44. Antennal flagellomeres one to twelve 442–470 µm long, thirteen 590–680 µm long, total length 1032–1150 µm. Eyes with dorsomedian extension; large frontal tubercles (length 16–18 µm), about 2.5 times as long as wide; 12–13 temporal setae; clypeus with 19–23 setae; lengths of palpomeres (in µm): 32–40, 38–44, 80–90, 98–118, 168–192, total length 416–484 µm.

Thorax. Length 1140–1230 µm. Scutal tubercle absent; 12–15 dorsocentrals in one row + group of 2–4 dorsocentrals posteriorly, 23–30 acrostichals, 2–3 prealars, 13 scutellars. Haltere with 6–8 setae.

Wing. Wing length 1780–1882 µm, width 548–575 µm; L/WR 3.21–3.24. Brachiolum with 1 seta, Sc with 1–5 setae, R with 46–56 setae, R1 with 50–67 setae, R4+5 with 80–105 setae, M with 16–28 setae, M1+2 with 74–92 setae, M3+4 with 47–63 setae, Cu with 18–39 setae, Cu1 with 24–34 setae, Postcubitus with 42–63 setae and An with 44–70 setae. Cell m with 35–44 setae (+20–26 setae on false vein), r4+5 with more than 200 setae, m1+2 with more than 200 setae (+43–55 setae on false vein), m3+4 with about 182 setae, cu with about 134 setae and an with about 142 setae.

Legs. Foreleg bearing single tibial spur (22–28 µm). Lengths of combs of mid tibia 20–23 µm (with 32– 35 µm long spur) and 21–23 µm (with 40–42 µm long spur); lengths of combs of hind tibia 23–28 µm (with 42–46 µm spur) and 22–26 µm (with 44–48 µm long spur). Lengths of leg segments and leg ratios as in table 2.

fe ti ta1 ta2 ta3 ta4 ta5 LR BV SV p1 910–990 508–560 1074–1190 610–638 550–562 478–495 180–190 2.11–2.15 1.36–1.46 1.23–1.39 p2 920–952 760–794 498–530 298–310 235–252 148–170 100–107 0.65–0.66 2.74–2.78 3.28–3.37 p3 953–1000 949–964 670–695 400–420 330–342 210–213 127–130 0.70–0.72 2.40–2.43 2.82–2.83 Abdomen. Length 2950–3060 µm.

Hypopygium ( Figs 16–19 ). Tergite IX 186–200 µm long with 9–10 median setae (not placed between anal tergal bands, not separated into groups, placed from well anterior to anal point base to close to anal point base), 18–20 apical setae, apparently without lateral teeth. T IX without microtrichia-free areas. Orolateral spine of T IX present, 2–3 µm long. Anal tergal bands separate, curved, short, not running parallel and ending well anterior to anal point base. Anal point 80–84 µm long, elongate with rounded to slightly pointed tip, with pair of well developed anal crests (34–50 µm long); field of microtrichia on entire surface between the crests; spines placed irregularly between anal crests; 2 shorter setae are present anteriorly between crests. Superior volsella with small to large field of microtrichia on anterolateral margin, anterior margin slightly curved, lateral and posterior margins curved, median margin concave, posteromedian corner projecting; 6–14 setae on dorsal surface, 2–3 setae on median margin and 1 seta on a ventral tubercle, close to anterior margin. Longitudinal axes of superior volsella and body at angle of 28–34°. Digitus pointed, triangular to somewhat cone-like, not extending or extending a little beyond margin of superior volsella. Median volsella 24–30 µm long, surpassing superior volsella but not reaching apex of inferior volsella, with 26–33 µm long simple lamellae and 30–40 µm long foliate lamellae. Inferior volsella 130–135 µm long, somewhat thick and slightly straight, distal part oval, only slightly swelled. Gonocoxite length 138–150 µm; gonostylus 150–156 µm, somewhat elongate, straight and thin; hypopygium ratio (HR) 0.92–0.98.

Pupa (n = 4)

Total length 5135–5800 µm.

Pupal exuviae pale brown, thorax and lateral muscle marks somewhat brownish.

Cephalothorax ( Figs 20–23 ). Frontal apotome smooth, with some wrinkles. Frontal setae short, 49–52 µm long, mounted apically on weakly developed cephalic tubercles; frontal warts absent. Pedicel sheath tubercle well developed. Thorax smooth, 1290–1320 µm long, with small teeth along median suture and granulation close to the basis of thoracic horn. Wing sheath with weakly developed nose, prealar tubercle well developed, somewhat rounded to quadrate and inwardly folded. Thoracic horn thin, 680–720 µm long, with spinules. Three precorneals not in triangular pattern, placed on a tubercle. Anterior precorneal 170–238 µm, Pc2 (196–204 µm) and Pc3 (212–248 µm) closer to each other, Pc3 thicker and longer; 1 median (136–154 µm) and 2 lateral antepronotals (100–110 µm, 1 seta base); 2 pairs of dorsocentrals, anterior pair 102–140 µm (thin) and 69–82 µm long (thick), posterior pair 100–104 µm (thin) and 94–96 µm (thick).

Abdomen ( Figs 24–25 ). Total length 3845–4480 µm. Tergites I and VII without armament. T II with median homogeneous shagreen, sparse/interrupted medially. T III with pair of long bands of long spines on posterior half of tergite, fields of fine shagreen lateral to spine bands, bands anteriorly straight, posteriorly curved outward. T IV with bracket-shaped pair of long bands of spines, anterior part with thin short spines directed to caudal and median, occasionally sparse or absent, posterior part with longer spines directed to oral. T V–VI with anterior pair of rounded spine patches. T VIII with fine anterolateral shagreen. T IX with anterior shagreen, sparse or interrupted on median part. Sternites I–VII apparently without armament. S VIII with fine oral-lateral shagreen. Conjunctives and pleura unarmed. Hook row 280–372 µm, about 1/2 width of tergite II. Pedes spurii A absent; pedes spurii B present on segment II, weakly developed. Posterolateral comb of segment VIII broad, 112–120 µm wide, consisting of 9–14 strong marginal teeth and 28–42 smaller ones. Abdominal setation: segment I with 2 dorsal taeniae and 1 dorsal seta, 0 L and 1 pair of ventral seta bases; segment II with 3 D, the most anterior and posterior setae somewhat taeniate, and two pairs of dorsal seta bases, 3 L and 4 V; segment III with 5 D, the most anterior and posterior setae somewhat taeniate, and two pairs of dorsal seta bases, 3 L and 5 V; segments IV–VII with 3 L, dorsal and ventral setae difficult to see; segment VIII with 1 D, 3 lateral taeniae and 1 ventral taenia. Anal lobe well developed, with complete fringe of 18–20 taeniae in single row and two pairs of dorsal taeniae. Tergites II–VIII with O-setae.

Distribution and ecological notes. Tanytarsus limneticus is a Nearctic species recorded from the USA. Caldwell et al. (1997) pointed out that "although originally listed by Hudson et al. (1990) as occurring in lakes, rivers, and streams, T. limneticus appears to occur only in lentic habitats. Larvae of similar, typically stream dwelling species (possibly Tanytarsus guerlus Roback or similar species), have probably been confused with T. limneticus ". Epler (2001) mentioned that most T. limneticus larvae collected by him are from bottom sediments of eutrophic ponds or slowly flowing rivers.

Figures

FIGURES 16 – 19. Tanytarsus limneticus Sublette, adult male. 16. Hypopygium, dorsal view. 17. Anal point, dorsal view. 18. Superior volsella and digitus variation. 19. Median volsella.

FIGURES 20 – 25. Tanytarsus limneticus Sublette, pupa. 20. Frontal apotome. 21. Thorax. 22. Thoracic horn. 23. Detail of thoracic horn armament. 24. Abdomen, dorsal view; dorsal setae of segments V – VII not drawn. 25. Posterolateral comb of abdominal segment VIII.