Zaitzevia rivalis Nomura, 1963

(Figs 2E, 15, 19F, 20H, I)

Materials examined. JAPAN: [HONSHU]: 4 larvae, Karakawa-gawa, Kawasimo, Izumo-shi, Shimane Pref., Honshu, 6.iii.2013, M. Hayashi leg. 2 larvae, Inu-dani, Nishihayashigi, Izumo, Shimane Pref., Honshu, 6.ii.2016, M. Hayashi leg. 2 larvae, same locality, 24.iii.2018, M. Hayahsi leg. 2 larvae, Miyama-gawa, Manda, Izumo, Shimane Pref., Honshu, 23.xii.2017, M. Hayashi leg.

Description. Body length of mature larva ca. 4.0 mm in expanded specimen.

Body elongate, narrowing from thorax to apex; convex dorsally and flattened ventrally; semicircular in cross section; spiracles on mesothorax and abdominal segments I–VIII. Body color black or dark brown, and appendages orange colored. Dorsal and ventral surfaces entirely not smooth with flat granules (Fig. 15D; Kodada et al. 2016: 583) and various types of setae.

Head visible from above, well exposed from prothorax; as wide as long; clypeus transverse, setose; without a pair of spines on both sides of clypeus (frontal tooth); vertex rugose with brush-like setae; eyes large but lens of stemmata absent. Antenna with three antennomeres; antennomere 1 shorter than antennomere 2, with short branched setae; antennomere 2 with long sensorial appendage; antennomere 3 short with small sensorial appendage. Maxillae and labium forming a unit (maxillolabial unit). Maxilla with four palpomeres; cardo small; stipes large; galea and lacinia separate, setose apically. Labium narrow with two palpomeres; ligula short and transverse; mentum long; submentum short and transverse.

Thorax not serrated on lateral sides; dorsum entirely not smooth with granules and flat brush-like setae (Fig. 19F). Prothorax wider than long, 2 times as long as mesothorax; with glabrous smooth area on dorsum; with seven ventral sclerites (one between coxae, two anteromedial, two anterolateral, and two posterolateral), procoxae not closed posteriorly; flat feather-like setae on hind margins. Meso- and metathorax transverse; metathorax slightly longer than mesothorax. Meso- and metathorax with five ventral sclerites (one large anteromedial, two anterolateral, and two posterolateral).

Abdomen 9-segmented; segments I–VIII transverse, dorsal surface entirely not smooth with granules; pleural sclerites on segments I–VII. Last segment (segment IX) longer than wide, gradually narrowing to apex; tergal surface with minute and coarse granules; with ridge on both sides (Fig. 15E); with longitudinal ridge on meson; apex notched; ventrally flat, with subpentagonal-shaped operculum, opercular claws, and anal gills.

Habitat. Upper stream reaches; larvae live in the gravel substrate.

Identification. The larva was identified by mitochondrial DNA sequences (Hayashi & Sota 2010).

Distribution. Honshu (type locality), Shikoku, Kyushu, Awaji Is., Goto Isls.: Fukue-jima Is.

Bibliography. Hayashi & Sota (2010: fig. 14).