Rheocricotopus (Rheocricotopus) reduncusoides, Namayandeh & Beresford, 2018

Namayandeh, Armin & Beresford, David V., 2018, A NEW SPECIES IN THE RHEOCRICOTOPUS (R.) EFFUSUS GROUP FROM CANADA WITH A REVIEW OF THE NEARCTIC SPECIES OF RHEOCRICOTOPUS AND PARAMETRIOCNEMUS (CHIRONOMIDAE: ORTHOCLADIINAE) Abstract, CHIRONOMUS Journal of Chironomidae Research 31, pp. 16-29 : 22-26

Rheocricotopus (Rheocricotopus) reduncusoides sp. n.

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( Figs 2a–c & 3a–c )

Material examined. Holotype: 1 ♂ slide-mounted in Canada Balsam, Bathurst Island, Nunavut , 75° 43’ N, 98° 25’ W, 10 July 1969, Coll. H.V. Danks, CH 1214 ( CNC). Paratypes: 4 ♂♂ slide-mounted in Canada Balsam, Bathurst Island, Nunavut , 75° 43’ N, 98° 25’ W, 10 July 1969, Coll. H.V. Danks, CH 1214 ( CNC). Rheocricotopus (Rheocricotopus) reduncus Saether and Schnell, 1988: 3 Paratypes, ♂♂, Jostedøla River at Inlet to small lake, Luster , Sogn and Fjordane, Norway, 23/7’ 86, A. Fjellheim and A. Schnell ( ZMB NO. 116 ).

Etymology: From Latin, reduncus meaning curved or hooked backward which refers to the shape of caudomedian projection of superior volsella, and the epithet of the most closely related species, and New Latin oides, referring to the likeness of form.

Diagnostic characters. HP small to indistinct. SVo with long caudomedian projections evenly curved, medially projected and opposing each other, apex slightly pointed. Sternapodme broad horizontal band. IVo simple, small, blunt, slightly dilated at the apex. AR = 0.75. BR 1–3 = 1.4, 1.2, 1.4. AnP 67 µm long with 13–19 setae. Gs with slight bent distally, CD developed, long and low. HR = 1.6.

Male (n = 5). Total length = 3.1mm

Coloration of slide-mounted specimen: Head and thorax dark brown, abdomen golden-brown, halter light brown with dorsolaterals darker, and wing yellowish brown.

Head. As in Fig. 2a . Antenna ( Fig. 2b ) with 13 flagellomeres, ultimate flagellomere 332 μm long, AR = 0.72–0.79 (0.75). Tentorium L = 152 µm. 4 Coronal setae. Temporal setae consisting of: 3 postorbitals, 1 inner verticals, 2 outer verticals present. Clypeus wider than long (L = 119 µm, W = 132 µm), bearing six setae. Palpomere p 1–5 lengths (µm): 51, 55, 79, 88, 144; sensilla clavata difficult to see on 3 rd palpomere.

Thorax. As in Fig. 2c . 7–8 antepronotals. 4–5 (4) acrostichals close to antepronotum (L = 11 µm). Dorsocentrals 7–9, uniserial (Ls = 57–69 µm). Prealars 2–3.

Wing. As in Fig. 3a . Wing with fine punctation. L = 2 mm, W = 0.5 mm. Squama with 4–5 setae, brachiulum with 1 seta, R with 5–6 setae, R 1 bare, R 4+5 with 2 setae. Costa slightly extends past R 4+5 (L = 30 µm).

Legs. Fore legs with tibial spur 41 µm long, mid tibial spurs 25 and 16 µ long, hind tibial spurs 44 and 23 µ long, comb with 15–17 setae. Pseudospurs are absent on t 1 and t 2 of mid and hind legs. Mid and hind femur with keel. Pulvilli well-developed, almost half as long as the claws. Lengths and proportions of legs in Table 2.

Hypopygium. As in Fig. 3b . Laterosternite IX with 6–7 setae (L = 25 µm). Phallapodme (59–66) 64 μm long; sternapodeme (90–105) 99 μm long. Anal point mostly hyaline, triangular with 13–19 setae, (56–89) 67 µm long. Superior volsella ( Fig. 3b–c ) with caudomedian projections long, finger-like, curved evenly before meeting medially, L = 84 µm. Inferior volsella simple triangular, lobe with blunt tip and slightly dilated at apex, L = 19 µm. Gonocoxite 278 µm long. Gonostyle curved with slight bent distally ( Fig. 3b ), L = 171 µm. Crista dorsalis long and low, megaseta L = 17 µm. HR = 1.6, HV = 1.8.

Remarks. This species is closely related to the Rheocricotopus (Rheocricotopus) reduncus . Combination of lower AR, lower BR, higher number of setae on AnP, longer AnP, a more evenly curved caudomedian projection of SVo ( Figs 3b–c ; compared to mainly bent in R. reduncus Fig. 4a–b ), apically dilated IVo, broad horizontal sternapodeme ( Fig. 3b ; compared to narrow arched in R. reduncus , Fig. 4c ), lower HR and HV separates the two species.

Based on the form of SVo this species belongs to the effusus group. Given the similarity of R. reduncus , R. reduncuiodes with other species within the effusus group a re-evaluation of the distinguishing characters is required to separate the species. In the effusus group the anal point length and thoracic chaetotaxy characters may not be sufficient to separate the species in this group. Saether and Schnell (1988) provided a somewhat better alternative for separating species in this group by listing the main comparative characters in a table. Following their example, we modified and corrected some of these characters and added few more ( Table 3 ).

A notable change to the characters given by Saether and Schnell (1988) is the AR range of R. reduncus . The Norwegian specimens of R. reduncus described by Saether and Schnell (1988) have AR 0.83–0.90 while Makarchenko and Makarchenko (2005) described the species from Far Eastern Russia with AR range of 1.16–1.17. This somewhat changes the state of characters given by Saether (1985) and discussed by Saether and Schnell (1988). If we are to consider Makarchenko and Makarchenko (2005) description of R. reduncus then the trend 8 of Saether’s (1985) classification of the genus, describing a male AR of 0.6–0.8, does not longer hold for this species. Consequently, the characteristic of AR should no longer be considered apomorphic for R. reduncus . For 1 st of trend 7 in Saether’s (1985) both R. reducncus and R. reduncusoides are synapomorphous (digitiform caudomedian projection) and symplesiomorphous for second (with small humeral pit). The broad horizontal sternapodeme of R. reduncusoides is autapomorphic for this species.

Figures

Figure 2. Rheocricotopus (R.) reduncusoides sp. n. male. a) head, b) antenna, c) thorax lateral view.

Figure 3. Rheocricotopus (R.) reduncusoides sp. n. male. a) wing, b) hypopygium, arrow indicates the sternapodeme, c) superior volsella caudomedian projection.

Figure 4. Rheocricotopus (R.) reduncus Saether and Schnell, male paratypes from Norway. a) caudomedian projection and inferior volsella, b) variation of the caudomedian projection and inferior volsella, c) sternapodeme (black arrow) and phallapodeme (white arrows).