Chostonectes nebulosus (Macleay, 1871)

Tsyrlin, Edward, Carew, Melissa & Alarie, Yves, 2020, Re-description of larvae of Chostonectes nebulosus (Macleay, 1871) (Coleoptera: Dytiscidae, Hydroporinae, Hydroporini, Sternopriscina) with an identification key to the known larvae of Chostonectes Sharp, 1882, Zootaxa 4718 (3), pp. 436-446: 439-443

publication ID

https://doi.org/10.11646/zootaxa.4718.3.11

publication LSID

lsid:zoobank.org:pub:1B6D3031-55E1-441A-9E34-4E8155C6A731

persistent identifier

http://treatment.plazi.org/id/866487FF-FFE9-FFA7-FF71-FCF5FA7DDEF2

treatment provided by

Plazi

scientific name

Chostonectes nebulosus (Macleay, 1871)
status

 

Larvae of Chostonectes nebulosus (Macleay, 1871)  

( Figs 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Material examined. Australia: Victoria: 5 larvae, 2 adults   , Australia, Victoria, Binks Road , 37.520S 144.239E, pond, 23 Dec 2018, E. Tsyrlin leg.; 9 larvae, 11 adults, same data, but on 20 Jan 2019 GoogleMaps   .

Molecular analysis. Neighbour joining analysis showed that the two specimens of C. nebulosus   grouped together with a 100% match between them ( Fig. 3A View FIGURE 3 ). The specimens of C. johnsonii   and C. gigas   separated from C. nebulosus   by an average genetic distance of 15.2% and 20.1%, respectively. The average genetic distance between C. johnsonii   and C. gigas   was 19.6%.

Diagnosis: Larvae of C. nebulosus   look similar to those of C. gigas   and C. johnsonii   recently described by Alarie (2019). They all possess the well-developed lateral projections of the nasale and a short siphon. C. nebulosus   can be recognized using the features mentioned below.

Head width and length smaller ( Table 2 View TABLE 2 ); HL/HW> 1.75 (instar II) and> 1.65 (instar III); NW/FRMW> 1.5 (instar II) and> 2 (instar III); HL/LAS> 2.6 (instar II) and> 2.5 (instar III); relatively long and narrow lateral projections of nasale ( Fig. 3C View FIGURE 3 ), with less than seven ventral tubercles distributed irregularly and not extending to base of lateral projections.

Redescription of instar III. Colour: Dorsally brown with yellow legs and head appendages; frontoclypeus pale with two light brown maculae mesally; frontal and lateral projections pale yellow; parietale yellowish laterally; head appendages predominantly pale yellow, A4 light brown, distal third of mandible light yellowish brown; thoracic and abdominal tergites light yellow; AB7 and AB8 brown except tip of siphon yellow; urogomphus predominantly brown, yellow proximally and over mid-length.

Body: Body shape sub-cylindrical, fusiform. Measurements and ratios are shown in Table 2 View TABLE 2 .

Head: Head capsule ( Fig. 2C View FIGURE 2 ). Occipital suture present. Width of nasale at least two times greater than minimum width of anterior projection. Lateral projections of nasale pointed downward at approximately 13 degrees in relation to horizontal plane, bearing one apical seta and five or six ventral tubercles ( Fig. 3C View FIGURE 3 ); parietale with 7–9 temporal spines ( Fig. 2C View FIGURE 2 ).

Thorax: Mesopleural region with a spiracular opening on each side.

Abdomen: Mesopleural region of segments I–VII with a spiracular opening on each side.

Chaetotaxy: Position and number of secondary setae ( Table 3 View TABLE 3 ); natatory setae present on dorsal margin of femora, tibiae, and tarsi ( Figs. 2 View FIGURE 2 D–2F).

Description of instar II. As instar III except as follows:

Body: Measurements and ratios that characterise the body shape are shown in Table 2 View TABLE 2 .

Colour: One large light brown patch in middle of frontoclypeus.

Head: Parietale with 5–6 lateral spines.

Thorax and abdomen: Spiracles absent.

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TABLE 3. Number of secondary setae on the legs of Chostonectes nebulosus (CNEB) compared to those of C. gigas (CGIG) and C. johnsonii (CJOH) (Alarie et al. 2019); CO, coxa; FE, femur; TA, tarsus; TI, tibia; TR, trochanter and ‘Total’ is the total number of setae.

    CNEB   CGIG     CJOH
Segment Sensillar Instar II Instar III Instar II Instar III Instar II Instar III
  series (n = 2) (n = 2) (n = 4) (n = 5) (n = 1) (n = 7)
ProCO D 3 5 3–5 6–11 5 4–7
  A 0 3 0 3–6 0 1–4
  V 1 4 1–2 7–9 1 4–8
  Total 4 12 4–7 18–26 6 10–18
ProTR Pr 1 1–2 1–2 2–4 1 1–2
  Di 0 0 0 0–2 0 0–1
  Total 1 1–2 1–2 3–5 1 1–3
ProFE NS(PD) 7 23–24 11–14 31–33 7 21–25
  AD 4–6 9–11 3–9 13–17 3 8–11
  AV 0 16–17 11–19 26–39 9 16–22
  PD 0 0–1 0 1–3 0 0
  PV 3 7–8 2–4 12–17 3 9–12
  Total 21–23 55–61 27–39 88–106 22 57–65
ProTI NS(PD) 8–10 19–20 15–18 32–36 9 15–21
  AD 3 5 4–6 6–9 5 4–8
  AV 0 2–3 0–1 2–4 0 0–1
  PV 2 3–4 3–5 5–6 2 3–6
  Total 13–15 30–31 24–27 47–54 16 23–34
ProTA NS(PD) 5–7 13–15 9–11 22–27 7 14–19
  AD 3–4 6–7 5–7 4–8 4 4–8
  AV 0 0 0–1 0–1 0 0
  PV 2–3 2–5 3–5 5–7 4 4–6
  Total 10–13 21–27 19–22 36–42 15 23–32
MesoCO D 3–5 4–6 3–5 8–13 5 6–10
  A 0 4 0 4–8 0 1–5
  V 2 5 1–2 8–12 2 4–8
  Total 5–7 13–15 5–7 23–33 7 12–21
MesoTR Pr 1 2 1–2 2–4 1 2–3
  Di 0 0 0 0–2 0 0–1
  Total 1 2 1–2 2–6 1 2–4
MesoFE NS(PD) 6–7 23–24 8–11 30–34 9 18–24
  AD 3–7 15–18 6–11 17–26 7 12–18
  AV 6 13–18 7–11 30–38 7 17–19
  PD 0 0 0 1–4 0 0
  PV 5 13 6–10 24–29 6 13–17
  Total 21–24 64–73 27–40 109–128 27 65–76
MesoTI NS(PD) 9–13 23 17–22 40–46 12 24–26
  AD 6–7 7–9 6–11 11–17 6 9–14
  AV 3–4 8 5–7 8–11 3 5–7
  PD 0 0 0 0–3 0 0–3
  PV 2 6–7 3–4 4–6 4 4–7
  Total 21–25 45–46 33–42 67–80 23 45–56
MesoTA NS(PD) 8–9 18–20 10–15 30–37 7 21–24