Description of the 5th instar larva of Hydropsyche sarpedon

Body length: Ranging from 15 to 18 mm (n = 9), (Fig. 10).

Head: Head in dorsal view (Figs. 11 & 12) rectangular, almost as long (1.5–1.9 mm; Mean = 1.76 mm; S.D = 0.19; n = 5) as wide (1.4–1.8 mm; Mean = 1.64 mm; S.D = 0.18; n = 5). Cephalic capsule (Figs. 11 & 12) reddishbrown in colour (chestnut). Frontoclypeal apotome (Fig. 13) nearly triangular, narrow and elongated, and pointed posteriorly. Anterior margin straight and slightly concave. Oral light spot absent from all examined specimens. Lateral light spots clearly visible and most noticeable. Lateral aboral light spots usually absent or not visible. Median aboral light spot blurred and joined with lateral ones. In ventral view (Fig. 14), two longitudinal bands distinctive, usually covering most of cephalic capsule. Submentum (Fig. 15) light brown (caramel), with lateral lobes short and wide (width-length ratio a:b: 0.18–0.23, mean = 0.21, S.D. = 0.01, n = 4).

Thorax. Notal plates light reddish-brown. Metanotum lighter than pronotum and mesonotum. Pronotum and mesonotum same colour as head. Median regions of posterior prosternites strongly pigmented, brown and irregularly oblong (Fig. 16); lateral regions of prosternites lighter, separated from median regions by light areas (Fig. 16). Ventral gills present on mesosternum and metasternum.

Abdomen. Abdominal gills absent from segment VII (Fig. 10). Abdominal segments with two types of gills: single-stemmed gills and bifid-stemmed gills. Ventrolateral gills with bifid stalk on each side of abdominal segments I–VI. Ventromesal gills with single-stemmed stalk on each side of abdominal segments I–VI. Lateral (pleural) gills on each side of abdominal segments III–VII. Ventral plates on abdominal segment VIII subtriangular, brown, with tapered, short, thick setae; posterior border with long, thick black bristles. Ventral plates IX subtriangular, brown; setae on posterior parts of plates IX longer and thicker than those of segment VIII; posterior borders with long, thick, black bristles (Fig. 17). Anal prolegs each with bent claw and cluster of tapered, dark, long slender setae. Ventral side of each anal proleg bearing series of tapered, long, dark setae lacking prominent setal sockets. Ventral membranous area covered with hair-like setae lacking spike-like setae.