Sinonychus tsujunensis Yoshitomi & Nakajima, 2012

(Figs 1A, 3, 18B)

Materials examined. JAPAN: [KYUSHU]: 2 larvae, Magome, Hitoyoshi-shi, Kumamoto Pref., Kyushu, 2.x.2011, J. Nakajima leg.

Description. Body length of immature larva ca. 1.6 mm.

Body elongate, narrowing from thorax to apex; convex dorsally and flattened ventrally; triangular in cross section, longitudinal ridge on meson sharp (Fig. 3E, F); spiracles on mesothorax and abdominal segments I–VIII. Body color brown, and appendages yellowish brown. Dorsal and ventral surfaces not smooth with flat granules (Fig. 3 A–D; 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 three 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. 18B). Prothorax wider than long, 2 times as long as mesothorax; with glabrous areas on basal half; with six ventral sclerites (two anteromedial, two anterolateral, and two posterolateral), procoxae not closed posteriorly; flat finlike setae on lateral margin; 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 minute granules; pleural sclerites on segments I–VII. Last segment (segment IX) longer than wide, gradually narrowing to apex; tergal surface with minute granules and coarse granules sparsely; without ridge on both sides; with longitudinal ridge on meson; apex truncate and slightly dentate; ventrally flat, with elongate subpentagonal-shaped operculum, opercular claws, and anal gills.

Habitat. Small stream, muddy gravel bottoms on riverbed (Yoshitomi & Nakajima 2012).

Identification. The larva was identified by association with adult S. tsujunensis from Kumamoto Pref., Kyushu, because the Sinonychus fauna of the islands includes only S. tsujunensis (Yoshitomi & Nakajima 2012) .

Distribution. Kyushu (type locality).

Bibliography. The larva of this species is described here for the first time.