Drusus radovanovici septentrionis

Description of the fifth instar larva of Drusus radovanovici septentrionis View in CoL

Larva. Case constructed completely from mineral particles ( Fig. 2 View FIGURES 2–9 ), slightly curving, total length 10.9-15.5 mm (N = 30). Overall body shape eruciform ( Fig. 3 View FIGURES 2–9 ), total length without case 11.0-16.8 mm (N = 30).

Head. Head capsule width 1.40-1.74 mm (N = 30), ellipsoid in shape and hypognathous ( Fig. 3 View FIGURES 2–9 ). Head colour brown, dorsally darker and laterally lighter, with granular sculpturing surface ( Figs. 3, 4, 5 View FIGURES 2–9 ). Genae of the parietals reddish-brown to yellow with lighter ring around each eye ( Figs. 4, 5 View FIGURES 2–9 ). Posterior part of dorsum with numerous, dark muscle attachment spots. Area with spinules (i.e. small spines) is positioned laterally at the inner eye margins on each side of the head capsule ( Figs. 6, 7 View FIGURES 2–9 ). Spinules positioned also laterally between eye and antennae. Spinules are visible only at higher magnifications (above 100 X), their size is approximately 0.03 mm ( Fig. 7 View FIGURES 2–9 ). Frontoclypeal apoptome bell-shaped with narrow central region ( Fig. 8 View FIGURES 2–9 ). Antennae short, dark brown, positioned on small, noticeable prominences, with one prominent lateral seta (setae no. 7 and no. 9) ( Figs. 4, 5, 6 View FIGURES 2–9 ).

Head with numerous setae, mainly positioned at marginal regions ( Figs. 4, 5, 6 View FIGURES 2–9 ). Three prominent setae present at lateral margins. Pair of light setae laterally of anterior margin of the head (setae no. 1) and two pairs of dark, prominent setae on each side of anterior region (setae no. 2 and no. 3); all this setae inside of frontoclypeal apoptome. One pair of light and short setae laterally of posterior region of frontoclypeal apoptome (setae no. 6), one pair of prominent, dark setae at central region of frontoclypeal apoptome (setae no. 5), and one pair of long and light setae laterally of anterior region of frontoclypeal apoptome (setae no. 4). Two setae are situated at each ring circling eyes, one light and short (anterior) and one dark and longer (posterior). On dorsal side three prominent and dark setae on each side of coronal suture, two laterally (setae no. 15 and setae no. 16), and one central (setae no. 17).

Labrum symmetrical, brown to reddish-brown, with setal brush at anterolateral margins and few thin setae on dorsal surface. Mandibles black, without teeth along edges, with median setal brush ( Fig. 9 View FIGURES 2–9 ). Two setae present laterobasally on mandibles ( Fig. 9 View FIGURES 2–9 ).

Labium and maxillae light-brown. Brown submental sclerites on labium, each with one prominent, dark seta. Maxillary palps five-segmented. Ventral apoptome bell shaped with pointed apex, brownish ( Fig. 10 View FIGURES 10–17 ).

Thorax. Pronotum dark brown with granular sculpturing surface ( Figs. 4, 5 View FIGURES 2–9 ). Posterior margin rounded, both posterior and lateral margins thick and darkly sclerotized ( Figs. 4, 5 View FIGURES 2–9 , 11 View FIGURES 10–17 ).

In lateral view anterior part (i.e. 50-60 %) of the pronotum ascending gently at first and then steeply (about 45°) creating hump in the posterior one-third ( Figs. 4, 5 View FIGURES 2–9 , 11 View FIGURES 10–17 ). Posterior end of pronotum forming saddle-like depression ( Fig. 5 View FIGURES 2–9 ). Mid-dorsal ecdysial line forming small concavity at hump, separating hump into two halves. Pronotum bearing dark setae, some of them long and conspicuous ( Figs. 4, 5 View FIGURES 2–9 , 11, 12 View FIGURES 10–17 ), following the anterior margin from mid-dorsal ecdysial line to lateral margin. Prosternal horn present.

Mesonotum sclerites brown, lighter than pronotum with dark muscle attachment spots, uneven (rugged) surface ( Fig. 12 View FIGURES 10–17 ). Long, dark setae at positions sa1, sa2 and sa3. Posterior and lateral margins thick and darkly sclerotized.

Metanotum with three pairs of metadorsal sclerites ( Fig. 12 View FIGURES 10–17 ). Anterior-median sclerites ellipsoid, distance between them smaller than their length ( Fig. 12 View FIGURES 10–17 ), covered by setae, mainly at median area of anterior margin, surface coloured similar to mesonotum. Posterior sclerites smaller and lighter than anterior sclerites ( Fig. 12 View FIGURES 10–17 ). Ellipsoid, with many setae and light spots on lateral margin. Group of setae present between posterior sclerites and between posterior and lateral sclerite. Lateral sclerites prolonged, sickle-shaped, lighter brown with dark median region and a group of setae at anterior region ( Fig. 12 View FIGURES 10–17 ).

Legs. Colour similar to that of head capsule and thoracic sclerites, brown to dark brown, with dark ventral and dorsal margins ( Fig. 12 View FIGURES 10–17 ). Complete dorsal edge of femur covered by large, dark setae. Setae at the dorsal edge of tibia present only in the distal region. Tarsal claws and tarsal claw basal seta and tibial spurs light brown, almost yellowish. Foreleg ( Fig. 13 View FIGURES 10–17 ) coxa and femur wide compared to those of mid- and hind-legs ( Figs. 14, 15 View FIGURES 10–17 ). Foreleg trochanter and femur with few yellow, short, stout, setae (spurs) at ventral margin. Ventral margin on the distal part of trochanter with a row of thin, yellowish setae (trochanteral brush) ( Fig. 13 View FIGURES 10–17 ). Mid- and hind-legs similar in shape and size ( Figs. 14, 15 View FIGURES 10–17 ), with slender coxa and femur. Trochanter of midleg with a few thin yellowish ventrodistal setae. Hind-legs with slender coxa and femur without yellowish, thin setae at ventral margin of trochanter.

Abdomen. Abdominal segment I with well developed dorsal hump and a pair of lateral humps. Numerous setae present anterior and lateral to dorsal hump. It is not possible to distinguish between setal areas sa1 and sa2, on dorsal side. With numerous ventral setae, some with small sclerites at bases. Lateral humps with few setae.

Single filamentous gills ( Fig. 3 View FIGURES 2–9 ) present on segments II-VII ( Fig. 32 View FIGURES 32–33 ). Dorsal pre-segmental gills present on segments II-VII and dorsal post-segmental gills present on segments II-VI. Ventral pre- and post-segmental gills present on segments II-VII; lateral pre- and post-segmental gills present on segments II-IV ( Fig. 32 View FIGURES 32–33 ). Lateral fringe extending from posterior quarter of segment II to anterior quarter of segment VIII.

Segment IX bearing irregular, semicircular, light brown dorsal sclerite, with distinct setae on posterior margin ( Fig. 16 View FIGURES 10–17 ). Anal proleg typical limnephilid-type ( Fig. 17 View FIGURES 10–17 ). Lateral sclerite prolonged, sickle-shaped, yellowish with small setae mainly in posterior region ( Fig. 17 View FIGURES 10–17 ). Group of setae situated closely to lateral sclerites, 2 pairs being distinct. Anal claws brown.