Stactobia distinguenda Botosaneanu & Nozaki 1996

Ito, Tomiko & Shimura, Noriyoshi, 2019, Notes on six microcaddisfly species (Trichoptera: Hydroptilidae) recorded for Japan, one a newly described species, Zootaxa 4629 (1), pp. 26-38 : 26-38

Stactobia distinguenda Botosaneanu & Nozaki 1996

( Fig. 6 )

Stactobia distinguenda Botosaneanu & Nozaki 1996 , 60–62, male, habitat, Japan (Honshu); Ito 2017, 219–220, male, Japan (Hokkaido, Honshu).

Final instar larva ( Figs 6 A–6M). Moderately depressed (flattened dorsoventrally), length up to 1.8 mm, sclerotized parts dark brown, other parts creamy.

Head ( Figs 6 B–6E). Subquadrate, sutures indistinct, width up to 0.28 mm, ratio of length to width about 1.1. Antennae near anterolateral corners, each with long apical seta. Setae 9 longest, about 1.5 times head width. Labrum symmetrical. Mandibles robust, each with 4 blunt teeth, mesal brush indistinct.

Thorax ( Figs 6 F– 6I). Dorsum of each segment covered by pair of large square thoracic nota; small round concavity at basal 1/4 of mesal edge of mesonotum, pair of concavities appearing as tiny hole; number of setae on each side about 30 on pronotum (~18 anteriorly, ~12 across middle), about 25 on each of meso- and metanota (~16 anteriorly, ~8 across middle). Prosternum with pair of transversely long sclerites near posterior margin and pair of small round sclerites at posterolateral corners; transversely elongate sclerites gradually broadened laterally, each with small cleft in lateral margin. Mesosternum with pair of short wide sclerites near posterior margin, sometimes indistinct.

Thoracic legs all robust, similar in length and form; basal seta of each tarsal claw slightly curved, subacute apically. Foretrochantin with subtriangular anterior and posterior halves. Pleura of meso- and metathoracic segments subrectangular, each slightly curved with small convexity at apical 1/3 of dorsal margin, pleural sutures indistinct.

Abdomen ( Figs 6 L–6M). Moderately depressed (flattened dorsoventrally), middle of abdomen swollen. Tracheal gills, humps, lateral fringes, or lateral tubercles absent. Subquadrate tergite and pair of setae on each of segments I–VII; tergites dark brown at anterior 2/3–3/4 and light brown at posterior 1/3–1/4; tergites of segments II–VII each with median small round area of chloride epithelia (dorsal ring of Marshall 1979; chloride epithelia? of Botosaneanu & Levanidova 1988); tergite VIII large, subquadrate with spinose posterior margin; tergite IX large, semicircular, posterior edge with regular ‘crenellations’ (modified flattened setae of Marshall 1979) or ‘crenels’ ( Botosaneanu & Levanidova 1988) medially and spines laterally. On segment X, lateral sclerites rectangular; paired anal legs strongly curved anterolaterad, anal claws without any accessory hooks.

Case ( Figs 6N, 6O ). Composed of ventral and dorsal valves; ventral valve forming almost flat sheet; dorsal valve forming convex dome carried tortoise-like, slightly larger than ventral valve; anterior and posterior hoods scarcely developed; made of silk together with few mineral particles especially at each end of dorsal valves.

Habitat and feeding. Larvae and pupae were found in the hygropetric zone. Gut contents comprised somewhat amorphous particles. The gut contents together with the robust mandibles with blunt teeth ( Fig. 6D ) suggest the larvae are scrapers adapted to stony substrata.

Specimens examined. Japan, Kyushu: Nagasaki: 3 males, 4 females, 2 pupae (male, female) , 6 larvae, Sasebo-shi, Maehata-cho , 17.v.2017, N. Shimura ; 4 larvae, same locality, 26.vii.2017, N. Shimura ; 1 pupa (female), 24 larvae, same locality, 4.x.2017, N. Shimura .

Distribution. Japan (Hokkaido, Honshu, Kyushu). New to Kyushu.

Remarks. The larvae of the genus Stactobia are unique in the family Hydroptilidae in having a pair of transversely rectangular dorsal sclerites on each of segments I–VII and large dorsal sclerites on each of segments VIII and IX ( Waringer & Graf 2011; Figs 6A, 6L, 6M ). The larvae of this species are distinguished from other congeneric Japanese species by the arrangement of the ventral sclerites of the thoracic sterna: A pair of transversely wide, submesal, subtriangular sclerites posteriorly and a pair of small round ones at the posterolateral corners on the prosternum, and a pair of transversely wide, linear, submesal sclerites posteriorly on the mesosternum ( Fig. 6G ). The case is slightly depressed dorsoventrally, broader medially, with very small anterior and posterior hoods, and made of silk with a few minerals dorsally ( Figs 6N, 6O ). These character states of cases are common to those of Japanese species of the S. nielseni Species Group: S. chichibu Ito 2017 , S. campire Ito 2017 , and S. urauchi Ito 2017 ( Ito 2017) .

Figures

FIGURE 6. Final instar larva and its case of Stactobia distinguenda Botosaneanu & Nozaki 1996. 6A–6M, larva: 6A, habitus, dorsal; 6B, head, left dorsolateral; 6C, head, ventral; 6D, left mandible, ventral; 6E, right antenna, right lateral; 6F, right halves of 3 thoracic nota, dorsal; 6G, 3 thoracic sterna, ventral; 6H, right foreleg and fore trochantin, right lateral; 6I, right foretarsal claw and basal seta, right lateral; 6J, right mesopleuron, right lateral; 6K, right metapleuron, right lateral; 6L, abdominal segments I–III, dorsal; 6M, abdominal segments VIII–X, left dorsolateral. 6N, 6O, case: 6N, dorsal; 6O, ventral. Scale bars for 6A and 6N = 1 mm.