Polypedilum (Pentapedilum) retusum Mukherjee, Mukherjee and Hazra, 2020

Mukherjee, Tuhar, Mukherjee, Bindarika & Hazra, Niladri, 2020, Revision of the Oriental species of Polypedilum Kieffer (Diptera: Chironomidae) with their phylogenetic relationship, Zootaxa 4820 (1), pp. 31-69 : 36-40

Polypedilum (Pentapedilum) retusum Mukherjee, Mukherjee and Hazra , sp. n.

GenBank accession number: MT012493

urn:lsid:zoobank.org:act:12D2FB13-557F-471D-B862-C3B3FD40EA64

Material examined. Holotype male with pupal exuvia [reared] labelled ‘ Polypedilum (Pe.) retusum Mukherjee, Mukherjee and Hazra, India, West Bengal, Paschim Bardhaman, Asansol (23.67, 87.02), 16.xi.2002, Coll. S. Nath’; paratypes 2 males data as holotype; 1 male with damaged pupal exuvia [reared] data as holotype; 3 males labelled ‘ Polypedilum (Pe.) retusum Mukherjee, Mukherjee and Hazra, India, West Bengal, Purba Bardhaman, Burdwan University Campus (23.25 N, 87.84 E), 28.x.2019, Coll. T. Mukherjee’.

Diagnostic characters. Male. Squamal setae 16–18; gonostylus blunt, apex little notched ending with 2 setae; superior volsella with gradually tapered apex bearing 3 basal and 1 large lateral setae near the base; inferior volsella slightly bifid; Pupa. Wing sheath with single row of pearls; cephalic tubercle cone shaped with a subapical seta; hook row occupying nearly 4/5th of segment width; presence of caudolateral spine; LS setae arranged on segments V–VIII: 4:4:4:5.

Etymology. The name “ retusum ” from the Latin word ‘ retusis ’, refers to slightly indented apex of both the inferior volsella and gonostylus of hypopygium; to be treated as adjective.

Male (n=7)

Total length 4.59–4.62, 4.6. Wing length 1.99–2.25, 2.12. Total length / wing length 2.05–2.3, 2.17.

Colouration. Thorax pale yellow with uniform colouration.Abdomen pale yellow with a dark brown pigmented non-uniform band at anterior 2/3 rd of abdominal tergite. Femur, tibia and tarsomere uniformly coloured, last two tarsomeres dark.

Head. Head width 600–670. Temporal setae 10–11 (IV 3, OV 4–5, Po 3). Clypeal setae 26–32. Frontal tubercle 120–180, 150 long. Eyes bare with dorsomedial extension of 150–220, 180. Antenna with 13 flagellomeres, ultimate flagellomere 780–810, 790; AR 1.85–1.92, 1.89. Length of Palpomeres (I–V): 30, 60, 150–160, 160–210, 510–600; fifth palpomere / third palpomere 1.3–1.1, 1.2. CA 0.56–0.54, 0.55; CP 1.18–1.17, 1.17.

Thorax. Acrostichals 8–12, 10; dorsocentrals 26–35, 30; prealars 6–7; scutellars 14–16, 15.

Wings ( Figures 1 A–B). Wing with dense macrotrichia. Brachiolars 6; R with 30–36, 33 setae, R 1 34–39, 37, R 4+5 55–64, 59 and Cu 64–66, 65, M 70 setae. Sc with setae. Squama with 16–18, 17 setae. Wing length 1.99–2.25, 2.12. Costal length 1.95–2.1, 2.02. CR 0.97–0.93, 0.95. VR 1.16–1.2, 1.18. Haltere bare with a dark spot at its apex.

Legs. Fore tibial scale blunt, 20 in length, width at apex of fore, mid and hind tibia: 60, 60 and 70 respectively. Hind tibial spur 40 and mid tibial comb 30 long.

Hypopygium ( Figures 1 C–D). T IX with 12–20, 16 setae. Anal tergite band separate, V shaped structure. Anal point 80–170, 120 long, 10–50, 30 broad at apex, little wide at base, medially constricted, parallel-sided with 2–3 lateral setae. Gonocoxite 60 long with 14–19, 16 setae. Gonostylus 110–160, 140 long with little notched blunt apex bearing 2 apical setae. Superior volsella gradually curved, 57–63, 60 long, 10 wide at base with pointed apex bearing 2–3 basal and 1 lateral setae at a distance of 18–21, 19 from base (SVR 0.68–0.69, 0.685). Inferior volsella partly bifid, 110–180, 146 long and 18–24, 21 wide at apex, with 12–15, 14 incurved setae and 3–4 setae at apex. HR 0.37–0.53, 0.45.

Pupa (n=2)

Total length of exuviae 2.79–2.92, 2.85. Antenna 8.70–9.00, 8.80 long. Wing sheath 9.60–9.75, 9.75 in length.

Colour. Pupal exuviae pale yellow, hookrow and caudolateral spine dark brown.

Cephalothorax ( Figure 2A ). Frontal warts absent; cephalic tubercle cone shaped, 18–21, 19 long, 36–45, 40 broad at base; frontal seta 30–33, 31.5 long, sub apical in position. Basal ring ( Figure 2B ) elliptical, 39 long, 21–24, 22 wide. Wing sheath with 25–29, 27 pearls in a single row ( Figures 2 C–D).

Abdomen ( Figure 2E ). T I bare. T II with anterior band of shagreen with posterolateral pedes spurii B. T III with dense row of anterior and sparse row of posterior spinules; T IV–V with patches of spinules at middle. Hookrow ( Figure 2F ) with ca. 68 hooklets in single row covering nearly 78–80% width of segment. Sternite IV with pedes spurii A present posterolaterally. T VI with dense spinules posteriorly and sparse at middle; T VII with weak band of spinules anteriorly. T VIII with 2 longitudinal bands of spinules. T II–IV with 3 hair–like L setae. T V–VII with 4, VIII with 5 LS setae. T V–VI with LS setae arranged in a similar pattern: 2 LS setae anterolaterally as a group and 2 LS posterolaterally also as a group; 4 LS setae at a distance of 0.11–0.14, 0.25–0.27, 0.6–0.8 and 0.89–0.93 of T V; 4 LS setae at 0.26–0.29, 0.31–0.33, 0.76–0.8 and 0.90–0.92 of T VI; 4 LS setae at 0.18–0.20, 0.27–0.29, 0.57–0.61 and 0.85–0.88 of T VII; 5 LS setae: 2 anterolaterally, 2 just anterior to caudolateral spine and 1 posterior to T VIII located at 0.19–0.2, 0.35–0.37, 0.59–0.62, 0.72–0.75 and 0.84–0.87. Anal lobe ( Figures 2 G–H) 200–240, 220 long, 230 wide with 54–56, 55 taeniae on each side. T VIII with a 30 long and 15 wide strong spine, posterolaterally ( Figure 2I ) lacking caudolateral spur.

Remarks. The new species differs from all known Indian species of the subgenus Pentapedilum due to the presence of a slightly notched inferior volsella. The Indian species P. robusticeps Guha & Chaudhuri, 1985 of the subgenus appears similar in having a broad anal point (28) and number of scutellars (16–18) to P. retusum sp. n. but differs in AR and shape of the inferior volsella. The new species disagrees with P. (Pe). macrotrichium Guha & Chaudhuri, 1981 in the number of brachiolars, squamal setae and well developed anal lobe. The present species shows closeness with P. (Pe). nodosum ( Johannsen, 1932) in maxillary palp and genitalia but both AR and HR are quite different. The barcode sequence showed ~5.6% divergence with P. (Pe.) nodosum ( Figure 3 ). The new species shows affinities with P. (Pe). wittei ( Freeman, 1955) in wing, squama and superior volsella while disposition of basal and outer seta of superior volsella, number of squamal setae and HR value are significantly different. A comparison between the allied Japanese species and the new species is given in table 2.

Ecology. The immature stages of the proposed new species were collected from pit lakes near Damodar River, Asansol. The larvae also inhabit in water bodies having anthropogenic activities. The pupae were taken out of ponds of Raniganj coal-belts which are a part of Lower Gondwana’s Panchet formation (298–251 mya) ( Gree 1940). The Raniganj coal fields are very old having deposits from the Carboniferous era. The area is part of degenerated eastern fringes of Chhotanagpur Plateau (Bandopadhyay et al. 2014). The vegetation of the surrounding area is mainly mixed grassland ( Reddy et al. 2015). Adult males were also collected from the University campus using LED light trap installed in an adjacent pond. The species is endemic to India till date.

Figures

FIGURES 1A–D. Adult male of Polypedilum (Pentapedilum) retusum sp. n. A, Wing (Photograph); B, Wing, scale: 1 mm; C, Hypopygium (Photograph); D, Hypopygium, scale: 0.01 mm.

FIGURES 2A–I. Pupa of Polypedilum (Pentapedilum) retusum sp. n. A, Cephalothorax, scale: 0.05 mm; B, Basal ring, scale: 0.1 mm; C, Wing sheath (Photograph); D, Wing sheath, scale: 0.1 mm; E, Abdomen (T I–VII), scale: 0.4 mm; F, Hookrow (T II), scale: 0.1 mm; G, T VIII and anal lobe (Photograph), scale: 0.1 mm; H, T VIII and anal lobe, scale: 0.2 mm; I, Spine at posterolateral corner of T VIII, scale: 0.05 mm.

FIGURE 3. Neighbor-Joining tree based on the COX1 gene sequences of Polypedilum (Pentapedilum) retusum sp. n. and four reference sequences from GenBank. Red circles mark nodes. Scale: 0.03 substitutions per nucleotide position.