Description of the final instar larva of Helicopsyche megalochari

Biometry. Body length ranging from 5.5 to 5.7 mm, head width from 0.57 to 0.61 mm (n = 6).

Head. Head capsule flattened dorsally, its surface very finely granulated and wrinkled, ovoid in shape, hypognathous with medium brown coloration (Figs. 1, 3). Pale muscle attachment spots on frontoclypeus and parietalia indistinct (Figs. 1–4). Large whitish ring around each eye (Figs. 1–3). Dorsal head capsule with complete set of primary setae (Fig. 1). Frontoclypeus elongated, with deep and semicircular lateral constrictions level with posterior edges of eyes (Fig. 1). In lateral view, head capsule with two carinae per parietale: (a) slightly curved dorsolateral carina starting from posterior end of central frontoclypeal constriction and meeting the frontocylpeal suture at antenna level (Fig. 2, white arrows); and (b) markedly curved ventrolateral carina starting halfway between eye and coronal suture and terminating at eye level (Fig. 1, white arrows). Antennae slender, short, originating from tiny conical base and situated two-thirds of distance from eye to anterior frontoclypeal margin; each consisting of 1 short apical sensilla and 1 short seta (Fig. 2, black arrow). Labrum light brown with darker lateral margins, broadly quadrangular, with rounded corners, with apical margin slightly concave (Fig. 1) and 6 pairs of primary setae in transverse row across middle of labrum. Submentum wedge-shaped, irregularly convex along anterior border, pointed laterally, rounded posteriorly and with conspicuous central posterior tip (Fig. 4). Mandibles short and asymmetrical, each with black central section, long seta on conical chalaza one-third distance from base of lateral margin, large and rounded terminal tooth, and subterminal crenelated cutting edge; mesal concavity of each mandible with groups of pinnate setae: Left mandible with proximal group long and fine, distal group short and thick and flexible; right mandible with one group of long and fine setae only (Figs. 5, 6).

Thorax. Pronotum dark brown, changing gradually to medium brown in its posterior third; with black and yellowish oval patches and muscle attachment spots; surface finely granulated (Fig. 7); anterior border with continuous row of long straight, slender, dark setae which are gradually replaced by yellowish and slightly thicker setae anterolaterally (Fig. 7); in total, 152–177 setae of varying lengths distributed over anterior two-thirds of each pronotal half. Prosternal horn lacking. Mesonotum trapezoidal, tapering posteriorly; sclerotization of mesonotum gradually fading posteriorly: anterior third light brown, with medium brown oval patches, posterior section almost entirely unsclerotized and whitish; anterior border with continuous row of long straight, dark setae (Figs. 7, 8); in total, 88–95 setae of varying lengths distributed over anterior two-thirds of each mesonotal half. Metanotum without sclerotization (Fig. 8); setation consisting of 6 setae in each setal area 1 (sa 1), 1 seta in each sa 2, and 9 setae in each sa 3 (Fig. 8).

Legs yellowish to light brown; coxa, femur and tibia of each foreleg much wider than those of mid- and hind legs (Figs. 9–11). Propleuron in lateral view with curved, s-shaped dorsal outline (Fig. 9, black arrow); anterior process (trochantin of Wiggins 1996) long, gradually tapering throughout its whole length (Fig. 9, black arrow), and with 1 thick terminal seta. Coxae with large groups of black setae. Proximal sections of trochanters without setae. Rows of minute spines and pale setae present along ventral edges of femora; pair of ventral edge setae on each meso- and metathoracic femur dark and widely spaced, each prothoracic femur with 2 pale and 2 dark ventral setae; pro- and mesothoracic tibiae each with 2 apical spurs, pro- and mesothoracic tarsi each with 1 apical spur and 1 apical seta. Tarsal claws of all legs curved, each with strong basal seta (Figs. 9–11).

Abdomen. Abdomen strongly curved ventrally and, to a lesser extent, also laterally (Fig. 21). First abdominal segment with one dorsal and one pair of lateral protuberances (Fig. 8), latter protuberances each with very dense cover of broad microspinules (Fig. 12). Large gland of unknown function beneath translucent cuticle of dorsal protuberance with its orifice distinctly visible near anterior border of this protuberance in H. bacescui (Botosaneanu 1956); this structure also clearly visible in H. megalochari (Fig. 8, black arrow). Gills lacking. Lateral line with lamellar setae (Fig. 13): 1 seta per side on segment I, 3 on segment IV, and 4 setae on each of segments V and VI; segment VIII with row of 1 1–13 tubercula ("forked lamellae" sensu Wiggins 1996) per side (Fig. 14). Segment IX with group of 4 setae per side (Fig. 16, dotted oval) and with terminal anal papilla ("papille sensorielle bilobée" sensu Botosaneanu 1956) (Fig. 16, black arrow). Anal prolegs short, light brown, each with 5 dorsal setae (Figs. 15, 16). Anal claws each with large ventral hook and comb-like dorsal process fitted with 6–8 tiny teeth (in Figs. 16, 17, only 5 of them visible).

Case. Case made of fine sand grains, helicoid, consisting of 3 right-handed coils (Figs. 18–20) and central columella (Fig. 21); in last instar cases (staged according to maximum head width of larvae) broadest and narrowest diameters ranging from 3.9 x 3.3 mm to 3.2 x 2.8 mm, height 2.4–2.6 mm (n = 6). In ventral view, with deep conical umbilicus (Fig. 18); in dorsal view apex with small opening (Fig. 19, white arrow), homologous with posterior opening of tubular case. Anterior opening circular (Fig. 20).