Halesus nurag

Waringer, Johann & Malicky, Hans, 2018, Larva of Halesus nurag Malicky 1974 (Trichoptera: Limnephilidae) and diagnostic key for the limnephilid larvae of Sardinia, Zootaxa 4425 (3), pp. 555-566: 556-557

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Halesus nurag


Description of the fifth instar larva of Halesus nurag 

Biometry. Body length of final instar larva ranging from 19.0 to 22.5 mm, head width from 1.89 to 1.92 mm (n = 2).

Head. Head capsule elongate, hypognathous, with dark brown coloration frontally and laterally, fading to orange brown posterolaterally and ventrally. With elliptical, dark brown muscle attachment spots on frontoclypeus and parietalia, strongly contrasting in color on posterior sections of parietalia ( Figs 1–3 View Figure ). Large areas of head surface covered by spinules ( Fig. 1 View Figure ). Whitish ring present around each eye ( Fig. 3 View Figure ); eyes slightly protruding ( Fig. 1 View Figure ). Head capsule with complete set of 18 pairs of primary setae ( Figs 1, 2 View Figure ). Frontoclypeus bell-shaped, with deep central constriction ( Fig. 1 View Figure ). Antennal bases roundish, situated halfway between eyes and anterior head margin ( Fig. 1 View Figure , white arrow). Antennae short, each consisting of 1 short cylindrical base and 1 short flagellum. At each parietal, 10 dorsal and 2 ventral primary setae present, with setae #9 and 14 long and conspicuous ( Fig. 1 View Figure ). Frontoclypeus with 6 pairs of primary setae, 3 of them along anterior border (#1–3). Labrum dark brown, with setal brush and primary setae #1–3 at anterolateral margins and primary setae #4–6 on dorsal area ( Fig. 1 View Figure ). Ventral apotome wedge-shaped, orange brown with dark brown anterior border; postgenal suture approximately 18% of apotome length ( Fig. 2 s View Figure ). Mandibles black, each with 5 terminal teeth along its edge (3 of them visible in Fig. 2 View Figure ); in addition, ridges present in central concavity ( Fig. 2 View Figure ).

Thorax. Pronotum ( Fig. 4 p View Figure ) completely covered by two thick sclerites meeting in a straight mid-dorsal ecdysial line; pronotal sclerites light brown, with strongly-contrasting dark brown ovoid muscle attachment spots; surface finely granulated ( Figs 3, 4 View Figure ). Its posterior and posterolateral margins thickened and bent dorsad, thereby creating semicircular groove with black stripes ( Fig. 3 View Figure ). With earlike posterolateral projection ( Fig. 3 View Figure ). Pronotal transverse groove at end of anterior 3rd distinct and with dark furrow ( Figs 3 View Figure arrow, 4). Along anterior border three setal rows present: (1) dense fringe of short, curved, fine, yellow short setae; (2) widely-spaced, continuous row of intermediate curved, pale setae; and (3) widely-spaced, continuous row of long, straight, dark setae ( Figs 3, 4 View Figure ). In total, 55–62 dark setae of varying lengths distributed over each pronotal half. Prosternal horn present ( Fig. 8 h View Figure ). Median brown central prosternite conspicuous, outlined like a flying bird’s silhouette: slightly pointed at anterior center, with winglike lateral sections and fan-shaped posterior extension ( Fig. 8 s View Figure ). Mesonotum ( Fig. 4 View Figure ms) completely covered by 2 light brown sclerites meeting in straight mid-dorsal ecdysial line; with dark brown muscle attachment spots. Their posterolateral and posteromedian margins strongly sclerotized and with black margins ( Fig. 4 View Figure ). Counts for mesonotal setae on each sclerite are as follows (nomenclature sensu Wiggins 1996): anterior setal group sa 1: 5–7, posterior group sa 2: 10–12, lateral group sa 3: 12–16. Metanotum ( Fig. 4 View Figure mt) partially covered by 3 pairs of light brown sclerites with dark brown muscle attachment spots. Anterior metanotal sclerites (sclerites of setal area 1, or sa 1 sensu Wiggins 1996) narrow and transversally elongate; their intermediate separation distinctly larger than length of each of them ( Fig 4 View Figure sa 1); with 12–16 setae per sclerite. Posterior metanotal sclerites (sclerites of setal area 2, or sa 2 sensu Wiggins 1996) broadly triangular, with 12–15 setae per sclerite and dense group of 8– 10 setae between them ( Fig. 4 View Figure , dotted oval). Lateral metanotal sclerites (sclerites of setal area 3, or sa 3 sensu Wiggins 1996) narrow, crescent-shaped, each with 12–15 setae concentrated at anterior third of sclerite ( Fig. 3 View Figure ). With small groups of 4–6 setae between each lateral (sa 3) and posteromedian sclerite (sa 2) ( Fig. 3 View Figure , dotted oval). Pleurae light brown, with black pleural suture; epimera of 2nd and 3rd legs with digiform ventral process bearing one or more setae. Legs light brown, with dark brown muscle attachment spots and numerous setae on coxae, trochanters, and femora ( Figs. 5–7View FIGURES 1–5View FIGURES 6–12); tibiae and tarsi with only small number of setae. Femora of 2nd and 3rd legs with several proximodorsal setae ( Figs 6, 7 View Figure arrows). Coxa, femur, and tibia of each foreleg much wider than those of mid- and hind legs Fig. 5 View Figure ). Additional setae lacking on anterior and posterior faces of mid- and hind femora ( Figs 6, 7 View Figure ). Ventral trochanteral brush at distal section of each trochanter present on all legs. Proximal section of all trochanters with only one primary seta each. Rows of minute spines present along ventral edges of femora; pairs of ventral-edge setae pale on fore femora, but dark on mid- and hind femora. Tibiae of all legs with 2 pale, stout subapical spines, tarsi with 2 long subapical setae; tarsal claws sickle-shaped, with stout basal spines ( Figs 5–7View FIGURES 1–5View FIGURES 6–12).

Abdomen. Abdominal segment I with 1 dorsal ( Fig. 4 View Figure dp) and 2 lateral fleshy protuberances ( Figs 4 View Figure lp, 9). Dorsal setal areas sa 1, sa 2, and sa 3 (sensu Wiggins 1996) fused, thereby creating continuous transverse row of 65– 75 setae on distinct medium brown basal sclerites anterior to dorsal protuberance ( Figs. 4 View Figure , 9 View Figure ); without setae posterior to dorsal protuberance ( Fig. 4 View Figure ). Lateral protuberance with large brown, smooth posterior sclerite without setae, but with 1–3 holes, usually 2 ( Fig. 9 View Figure , dotted oval). Lateral protuberance setae consisting of dorsal group of 12–16 setae and single ventral seta. On abdominal sternum I, setal areas sa 1 and sa 2 fused, creating continuous central field of approximately 110 setae, about half of them with medium-sized, brown basal sclerites widely separated from each other; setal areas sa 3 situated ventral of lateral protuberances and separated from sa 1 and sa 2, consisting of 15–20 setae, about half of them with medium-sized, brown basal sclerites ( Fig. 10 View Figure ). Abdominal segments II–VII with 2 dorsal setae each. On abdominal dorsum VIII, number of posterodorsal setae (pds) typically 10, with 6 long and remainder short ( Fig. 12 View Figure pds). Only 1 posterolateral seta ( Figs 11, 12 View Figure , black arrows) and 2 tiny ventral setae present on each half of abdominal dorsum IX. Light brown abdominal tergite IX semicircular, with medium brown muscle attachment spots ( Fig. 12 View Figure ); along its posterior border, 7–9 long and several shorter setae present, 1 of these long setae having position of central intermediate seta. Anal prolegs of limnephilid type, yellowish brown, with medium brown muscle attachment spots. Lateral sclerite ( Fig. 11 View Figure ls) with 5 dark dorsal and row of 5 dark ventral setae, 3 of latter very strong and prominent. Ventral sole plate ( Fig. 11 View Figure vsp) with black dorsal stripe and single anterior seta. Anal claw basal sclerite Fig. 11 View Figure ac) with 3 tiny pale ventral setae and 3 darker dorsal setae; anal claw dark brown, with 1 small dorsal accessory hook ( Fig. 11 View Figure ).

All gills single filaments ( Fig. 13 View Figure ). Dorsal gills present at most from segment II (presegmental position) to segment VII (presegmental position). Ventral gills ranging from segment II (presegmental) to segment VII (postegmental). Lateral gills present from segment II (presegmental) to segment IV (postsegmental position). Lateral fringe extending from anterior border of abdominal segment III ( Fig. 14 View Figure lf) to end of abdominal segment VIII. With large oval chloride epithelia on abdominal sterna II–VII ( Fig. 13 View Figure , dotted oval). Abdominal segments II– VII with 3–7 forked lamellae immediately dorsal of lateral fringe ( Fig. 14 View Figure fl).

Case. Larval case 27.5–33.0 mm long (n = 2), very slightly curved and almost untapered (width at anterior opening 7.0– 7.5 mm and at posterior opening 5.3–7.8 mm). Cases consist of mix of mostly detrital particles of unequal size arranged longitudinally and sometimes few sand grains; typically also including fibers, conifer needles or longitudinal detritus protruding from posterior end ( Fig. 15 View Figure ).