Stactobiella tshisjakovi

Stactobiella tshisjakovi (Arefina & Morse, in Arefina et al. 2002)

(Fig. 2)

Stactobia tshistjakovi Arefina & Morse, in Arefina et al. 2002, 103–104, male, Russian Far East (Khasansky); Arefina & Armitage 2003, 17, Russian Far East (Sakhalin).

Stactobiella tshistjakovi: Arefina 2004, 209; Ito et al. 2010, 57, Japan (Hokkaido); Ito 2013, 51, 80, Japan (Hokkaido); Potikha & Vshivkova 2016, 364, Russian Far East (Primorye); Ito 2017a, 40, Japan (Hokkaido); Ito 2020, 562–563, male, female, Japan (Hokkaido, Honshu).

Final instar larva (Figs 2A–2G). Slightly compressed laterally, up to 1.7 mm long.

Head. Almost quadrate, sides subparallel, width up to about 0.2 mm; width:length:depth about 1.00:1.05:0.95; light brown, without any color patterns; longest pair of setae situated near mesal sides of eye spots (seta 9 of Wiggins 1996) about 2.8 times head width and 2.3 times head length; anterior ventral apotome wide, triangular. Coronal suture distinct. Anterior apotome shallowly triangular, cardo and posterior apotome indistinct. Antennae situated near anterolateral corners, each with seta near mid-length and sensillum apically.

Thorax. Pronotum completely covered with pair of rectangular tergites; meso- and metanota each broadly covered with pair of rectangular tergites; pronotum light brown with dark lateral and posterior edges, meso- and metanota each with dark anterolateral corners and dark posterior edges; number of setae on each tergite, about 15 on pronotum, about 12 on mesonotum, and about 10 on metanotum; ventral sclerites absent. Three thoracic legs short and subequal tarsal claws stout, sharply curved, each with slightly curved and thickened blunt basal spur (indicated by arrow on Figs 2E, 2F).

Abdomen. Slightly compressed laterally, distended, segments gradually enlarging from I to IV, then decreasing, curvature of abdomen slight; dorsal chloride epithelia on segments II–VIII; without sclerites on segments I–VIII; single large dorsal sclerite on segment IX; pair of square dorsolateral sclerites on segment X; segments IX and X without respiratory structures; anal claws without accessary hooks.

Case (Figs 2H, J). Compressed laterally, composed of two ellipsoidal valves, partially sealed on dorsal and ventral edges, with slit openings at anterior and posterior edges, slits both very deep on ventral margins; valves made of filamentous algae, rarely combined with few fine sand grains, algal filaments arranged parallel with each other and those of each half parallel with convex ends of case. Length up to 2 mm.

Specimens examined. 4 final instar larvae, Japan, Hokkaido, Horokanai-cho, Shumarinai, a small tributary of Shumarinai-gawa River (44.299444 N, 142.155833 E, 270 m above sea level), 6.vi.2009, A. Ohkawa & Y. Takashima; 31 final instar larvae, same locality, 22.vi.2021, T. Ito.

Habitat. The larvae were collected in a small stream, in a section 2–4 m wide and 1–5 cm deep, and shaded by riparian trees. The stream base is cobbles, pebbles and culverts (tunnel carrying the stream under a road and a railway, built in the 1950s). Adults of more than 50 caddisfly species including seven micro-caddisflies [Hydroptila asymmetrica Kumanski 1990, H. botosaneanui Kumanski 1990, H. chinensis Xue & Yang 1990, H. phenianica Botosaneanu 1970, H. spinosa Arefina & Armitage 2003, Oxyethira mekunna Oláh & Ito 2013, O. shumari Ito & Oláh 2017, and Stactobiella tshistjakovi (Arefina & Morse 2002, in Arefina et al. 2002)] were collected at the site by light trap, sweep-netting, and Malaise trap (Ito 2017a). The larvae of S. tshisjakovi were abundant in the very shallow (less than 1 cm deep) and fast-flowing (about 40–50 cm /second) part of a culvert, but absent in the deeper (exceeding 3 cm depth) part with similar substrates.

Distribution. Russian Far East (Primorye, Sakhalin), Japan (Hokkaido, Honshu).

Japanese name. Sawa-hime-tobikera.

Remarks. The final instar larvae and their cases of genus Stactobiella are generally similar to those of species of Hydroptila Dalman (Wiggins 1996; Ito 2021b) but larvae of Stactobiella are distinguished from the latter by the absence of the three filamentous gills on abdominal segments IX–X and the presence of a thick blunt basal spur on the mesal base of the strongly curved claw of each thoracic leg (Wiggins 1996). Similar blunt basal spurs are also present on tibiae of the larvae of the Palearctic genus Stactobia McLachlan (Graf & Waringer 2002; Ito 2017b), but Stactobiella can be distinguished from Stactobia by the absence of small tergites on abdominal segments I–VII; these are conspicuous on larvae of Stactobia.

The larva and case of S. tshistjakovi are similar to those of known the congeneric species, European S. risi (Felber 1908) (Graf & Waringer 2002; Waringer & Graf 2011), the North American S. palmata (Ross 1938) (Ross 1944), and an unassociated North American species illustrated by Wiggins (1996). However, larvae of S. tshistjakovi differ from those of S. risi by the shape of the basal spur of each tarsal claw which is slightly curved, thickened, slightly clavate, and blunt in S. tshistjakovi, but almost straight and subacute apically in S. risi (Graf & Waringer 2002; Waringer & Graf 2011). The larva of S. tshistjakovi also differs from the unassociated North American species in the length of the longest setae on the head: 2.3 times the head length in S. tshistjakovi, but shorter than the head length in the North American species (Wiggins 1996). It is impossible to compare the larva of S. tshistjakovi with that of S. palmata, due to the scant description in which only length and color of sclerites were given by Ross (1944). This is the first description of the larva of an Asian Stactobiella species.