Halesus nurag, Malicky, 1974

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

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 ). Large areas of head surface covered by spinules ( Fig. 1 ). Whitish ring present around each eye ( Fig. 3 ); eyes slightly protruding ( Fig. 1 ). Head capsule with complete set of 18 pairs of primary setae ( Figs 1, 2 ). Frontoclypeus bell-shaped, with deep central constriction ( Fig. 1 ). Antennal bases roundish, situated halfway between eyes and anterior head margin ( Fig. 1 , 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 ). 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 ). Ventral apotome wedge-shaped, orange brown with dark brown anterior border; postgenal suture approximately 18% of apotome length ( Fig. 2 s ). Mandibles black, each with 5 terminal teeth along its edge (3 of them visible in Fig. 2 ); in addition, ridges present in central concavity ( Fig. 2 ).

Thorax. Pronotum ( Fig. 4 p ) 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 ). Its posterior and posterolateral margins thickened and bent dorsad, thereby creating semicircular groove with black stripes ( Fig. 3 ). With earlike posterolateral projection ( Fig. 3 ). Pronotal transverse groove at end of anterior 3rd distinct and with dark furrow ( Figs 3 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 ). In total, 55–62 dark setae of varying lengths distributed over each pronotal half. Prosternal horn present ( Fig. 8 h ). 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 ). Mesonotum ( Fig. 4 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 ). 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 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 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 , 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 ). With small groups of 4–6 setae between each lateral (sa 3) and posteromedian sclerite (sa 2) ( Fig. 3 , 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. 5–7 ); tibiae and tarsi with only small number of setae. Femora of 2nd and 3rd legs with several proximodorsal setae ( Figs 6, 7 arrows). Coxa, femur, and tibia of each foreleg much wider than those of mid- and hind legs Fig. 5 ). Additional setae lacking on anterior and posterior faces of mid- and hind femora ( Figs 6, 7 ). 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 5–7 ).

Abdomen. Abdominal segment I with 1 dorsal ( Fig. 4 dp) and 2 lateral fleshy protuberances ( Figs 4 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 , 9 ); without setae posterior to dorsal protuberance ( Fig. 4 ). Lateral protuberance with large brown, smooth posterior sclerite without setae, but with 1–3 holes, usually 2 ( Fig. 9 , 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 ). 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 pds). Only 1 posterolateral seta ( Figs 11, 12 , 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 ); 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 ls) with 5 dark dorsal and row of 5 dark ventral setae, 3 of latter very strong and prominent. Ventral sole plate ( Fig. 11 vsp) with black dorsal stripe and single anterior seta. Anal claw basal sclerite Fig. 11 ac) with 3 tiny pale ventral setae and 3 darker dorsal setae; anal claw dark brown, with 1 small dorsal accessory hook ( Fig. 11 ).

All gills single filaments ( Fig. 13 ). 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 lf) to end of abdominal segment VIII. With large oval chloride epithelia on abdominal sterna II–VII ( Fig. 13 , dotted oval). Abdominal segments II– VII with 3–7 forked lamellae immediately dorsal of lateral fringe ( Fig. 14 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 ).

Figures

FIGURES 1–5. Halesus nurag Malicky 1974, 5th instar larva. 1, head, frontal (small white numbers refer to setal positions; small white circle refers to alveolus of parietal seta #11; arrow points to right antenna); 2, head, ventral (small black and white numbers refer to setal positions; s = submentum); 3, head and thorax, right lateral (p = pronotum; ms = mesonotum; mt = metanotum; arrow points to transverse rim at anterior 3rd of pronotum; white circle refers to setal group between setal areas sa2 and sa3); 4, thorax and abdominal segment I, dorsal (dp = dorsal protuberance; lp = lateral protuberance; ms = mesonotum; mt = metanotum; p = pronotum; sa1–sa3 = setal areas 1–3; white circle refers to setal group between pair of sa2 setal areas 2); 5, left foreleg, posterior face. Scale bars: 1.0 mm.

FIGURES 6–12. Halesus nurag Malicky 1974, 5th instar larva. 6, left midleg, posterior face (arrows point to proximodorsal setae); 7, left hind leg, posterior face (arrows point to proximodorsal setae); 8, head and prosternum, ventral (h = prosternal horn, s = prosternite); 9, abdominal segment I, right lateral (black circle refers to single posterior sclerite of lateral protuberance); 10, abdominal segments I and II, ventral (sa1–3 = setal areas 1–3); 11, abdominal segments VIII–X with anal proleg, right lateral (ac = anal claw with dorsal accessory hook; ls = lateral sclerite of anal proleg; vsp = ventral sole plate; arrow points to right posterolateral seta; dotted oval refers to ventral setae); 12, abdominal segments VIII–X, dorsal (pds = posterodorsal setae on abdominal segment VIII; arrows point to posterolateral setae). Scale bars: 1.0 mm.

FIGURES 13–19. Halesus, Stenophylax, and Leptodrusus spp., 5th instar larvae. Figures 13–16, Halesus nurag Malicky 1974, 5th instar larva: 13, sternum of abdominal segment V, ventral (black oval refers to chloride epithelium); 14, abdominal segment III, right lateral (lf = starting section of lateral fringe; fl = row of forked lamellae 1–7); 15, larval case, right lateral; 16, right mandible, right lateral. Figures 17–18, Leptodrusus budtzi (Ulmer 1913), 5th instar larva: 17, right mandible, right lateral; 18, abdominal segments VIII–X with anal proleg, right lateral (black oval refers to posterolateral setae). Figure 19, Stenophylax permistus McLachlan 1895, 5th instar larva, abdominal segments VIII–X with anal proleg, right lateral (black oval refers to single posterolateral seta). Scale bars: 1.0 mm (except Figures 14, 16: 0.5 mm).