Cladotanytarsus acornutus Jacobsen et Bilyj

Puchalski, Mateusz & Giłka, Wojciech, 2017, Cladotanytarsus Kieffer (Diptera: Chironomidae): several distinctive species reviewed on the basis of records from Canada and USA, Zootaxa 4242 (2), pp. 344-358 : 345-347

Cladotanytarsus acornutus Jacobsen et Bilyj

( Fig. 1 )

Cladotanytarsus acornutus Jacobsen et Bilyj, 2007 : Jacobsen & Bilyj 2007: 146 (adult male and female, pupa, larva; USA, Florida), Epler 2014: 20, 22, 23 (larva, in key; all stages, remarks; USA, Florida).

Material examined. CANADA. ONTARIO . North Kawartha, Julian Lake N of Peterborough (swarm at edge of lake), August 1968, 10 males, leg. John A . Spence. Waterloo, shallow pond, 2 males, leg. John A. Spence. USA. SOUTH CAROLINA. Oconee Co., Hartwell Lake, Clemson , 7 July 1973, 1 male, leg. P . Hudson. Oconee Co., Keowee Reservoir , 21 April, 1975, 1 male (abdomen with hypopygium), 11 May 1975, 1 male, 30 May 1975, 1 male, 6 June 1975, 3 pharate males in 3 Pex, leg. P. Hudson. Ex coll. M. & J.E. Sublette. Deposit in DEUM.

Diagnostic description (supplementations to the original description).

Adult male. Head. AR 0.68–0.98. Frontal tubercles small, cylindrical, 5–15 µm long. Length of palpomeres 2– 5 (in µm): 25–35, 50–95, 70–100, 110–160. Clypeus semicircular, with 12–17 setae.

Thorax chaetotaxy. Ac usually absent, up to 3 if present (n = 3); Dc 6–8; Pa 1; Scts 2–4.

Wing. Length 1150–1500 µm. Shape, venation pattern and chaetotaxy as in original description; R, R1 and R4+5 rarely with macrotrichia and m1+2, r4+5 sometimes with sparse macrotrichia distally, VR Cu 1.16–1.49 (1.25).

Legs. Fore leg tibia with straight spur ca. 20 µm long. Each comb of mid and hind leg tibiae bearing straight or slightly curved spur: ca. 15–20 µm long on mid leg and up to 25 µm long on hind leg. Basitarsus of mid leg usually without sensilla chaetica, sometimes with 2–4 hook-shaped sensilla present (n = 7). For lengths of leg segments and leg ratios, see Table 1 .

Hypopygium ( Fig. 1 ). Gonostylus ca. 75 µm long, with apical seta placed on conical tubercle. Anal tergite with V-type separated bands and 4–10 setae arranged in irregular rows or setae dispersed at base of anal point. Anal point variable in shape, elongate, evenly tapering towards apex, with up to 6 spinulae between narrow crests or crests not developed ( Fig. 1 A, C). Superior volsella pear-shaped in dorsal aspect, with more on less narrowed distal part, bearing field of microtrichia on proximal (swollen) part, 6–9 dorsal setae and 3 long setae placed on conical tubercles at base. Digitus straight or slightly curved, long, extending far beyond superior volsella, with finger-like tip ( Fig. 1 A, D). Stem of median volsella relatively long (ca. 35 µm), straight or finely curved, as shown in Fig. 1 E, bearing several setiform and 4–5 furcate lamellae: 3–4 strong and 1–2 weaker ( Fig. 1 B, E). Inferior volsella with slight lateral knee-like extension at base, distinctly curved and posteromedially or medially directed, darkly pigmented dorsomedian ridge narrow ( Fig. 1 A, B, F).

Remarks. In the Sublettes’ collection of North American Cladotanytarsus , nearly 20 adult and pharate male specimens as well as their pupal exuviae were identified as C. acornutus . Records of this species have so far been confined to the Florida Everglades, where C. acornutus has been defined as one of the most abundant chironomids and an outstanding indicator of nutrient-poor and minimally disturbed habitats ( Jacobsen & Bilyj 2007, Epler 2014). Our records from southern Ontario, Canada, and from the northern part of South Carolina, USA, provide evidence that the geographical distribution of C. acornutus is wider than that previously assumed. According to Epler (op. cit.), larvae outside of the Everglades believed to be this species are determinable after association with a pupa that lacks a thoracic horn and/or with an adult male that has weak hypopygial anal point crests and lacks acrostichal setae. Indeed, the currently examined specimens have thin or reduced crests, and the acrostichals are usually absent (at most 3 if present). The pupal exuviae are also consistent with those originally described, except for a TII hooklet row that consists of a slightly larger number of hooklets at 1/2 width of the segment; none of the pupal exuviae examined have a thoracic horn.

Figures

FIGURE 1. Cladotanytarsus acornutus Jacobsen et Bilyj, 2007, male. A, B — hypopygium in dorsal (A) and ventral aspect (B); C — anal point (variation); D — superior volsella and digitus (variation); E — median volsella and its stem (variation); F — inferior volsella, typical structure (D—magnified ca. 2 times relative to A; E, F—magnified ca. 3 times relative to A).

Tables

TABLE 1. Lengths (µm) of leg segments and leg ratios of male Cladotanytarsus acornutus Jacobsen et Bilyj, 2007.

	fe	ti	ta1	ta2	ta3	ta4	ta5	LR
p1	480–650 (530)	265–375 (310)	525–710 (595)	250–370 (315)	235–295 (260)	150–215 (170)	65–105 (90)	1.75–2.16 (1.89)
p2	480–640 (555)	390–510 (440)	215–265 (235)	120–160 (135)	85–110 (95)	60–80 (70)	50–70 (60)	0.50–0.55 (0.53)
p3	560–685 (610)	540–655 (600)	345–430 (375)	220–265 (240)	160–225 (200)	130–150 (140)	80–95 (90)	0.59–0.67 (0.62)