Limnephilus minos Malicky 1970

Waringer, Johann & Malicky, Hans, 2019, The larvae of Limnephilus minos Malicky 1970 and Mesophylax impunctatus aduncus (Navás 1923) (Trichoptera: Limnephilidae), including a discriminatory matrix for the Greek limnephilid larvae with multifilament gills, Zootaxa 4612 (2), pp. 187-204 : 188-189

Description of the fifth instar larva of

Limnephilus minos Malicky 1970

( Figs 1–14 )

Biometry. Body length of 5th instar larva 16.5–17.8 mm, head width 1.34–1.42 mm (n = 4).

Head. Head capsule nearly round, hypognathous, granulate, dark brown, with dense cover of microspinules (length approximately 0.01 mm) over wide areas of parietalia and around central constriction of frontoclypeal apotome ( Figs 1, 2 ). Dark brown, elliptical muscle attachment spots inconspicuous. Whitish ring present around each eye ( Fig. 3 ). Head capsule with complete set of 18 pairs of primary setae: frontoclypeal apotome with setae #1–6, parietalia dorsally with setae #7, 9–17, ventrally with setae #8 and 18; setae #9 and 14 strong and prominent ( Figs 1, 2 ). Frontoclypeus bell-shaped, with deep central constriction ( Fig. 1 ). Antennal bases nearly round, situated halfway between eye and anterior head margin ( Fig. 1 a ). Antennae short, each consisting of 1 short cylindrical base and 1 short flagellum. Labrum dark brown; primary setae #1–4 near anterolateral margin, setae #5–6 on dorsal area ( Fig. 1 ). Cardines dark brown ( Fig. 2 c ). Ventral apotome amphora-shaped, light brown, with wedge-shaped dark brown anterior border; postgenal suture approximately 20% of apotome length ( Fig. 2 va). Mandibles black, each with 5 terminal teeth along its edge (3 of them visible in Fig. 1 ), and with ridges in central concavity.

Thorax. Pronotum ( Fig. 4 p ) finely granulate, dark brown, with dark, oval muscle attachment spots and posterior border bent dorsad, thereby creating black, semicircular groove ( Fig. 3 ). End of anterior 3rd of pronotum with dark transverse rim ( Fig. 3 , arrow). Heavily sclerotized pair of pronotal plates meeting medially in narrow, straight ecdysial suture ( Fig. 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, 45–57 dark setae of varying lengths distributed over each pronotal half. Prosternal horn present ( Figs 2, 3 ph). Yellowish brown central prosternite conspicuous, broadly quadrangular, approximately 2.3 times wider than long; with pairs of brown spots along anterior and posterior borders ( Fig. 2 cs). Lateral prosternites distinctly separated from central prosternite, kidney-shaped, dark brown ( Fig. 2 ls).

Mesonotum ( Fig. 4 ms) dark brown, completely covered by pair of sclerites meeting in straight mid-dorsal ecdysial line; with dark brown muscle attachment spots, especially along each sclerite’s midline. Posterolateral and posteromedian margins strongly sclerotized and black ( Fig. 4 ms). Counts for mesonotal setae on each sclerite as follows (nomenclature sensu Wiggins 1996): anterior setal group sa 1: 5–7, posterior group sa 2: 7–11, lateral group sa 3: 15–19.

Metanotum ( Fig. 4 mt) mostly unsclerotized, whitish; small brown sclerites of setal area 1 (sa 1 sensu Wiggins 1996) ovoid; their intermediate separation distinctly wider than the longitudinal length of each of them ( Fig 4 sa 1); with 4–6 setae per sclerite. Sclerites of sa 2 brown, shortly rectangular or trapezoidal, with 8–15 setae per sclerite ( Fig. 4 sa 2). Dark brown sclerites of sa 3 narrow, crescent-shaped, each with 15–18 setae concentrated at anterior third of sclerite ( Fig. 4 sa 3). Without setae between paired sa 2, and between sa 2 and sa 3 on each side ( Fig. 4 ).

Pleurae light brown, with black pleural suture; epimera of 2nd and 3rd legs with digitiform ventral process.

Legs medium brown, with numerous setae on coxae, trochanters, and femora ( Figs. 5–8 ); tibiae and tarsi with only small number of setae. Femora of 2nd and 3rd legs each with one proximodorsal seta ( Fig. 6 arrow). Coxa, femur, and tibia of each foreleg ( Fig. 5 ) much wider than those of mid- and hind legs. Additional face setae lacking on anterior and posterior faces of mid- and hind femora ( Figs 6, 8 ). Anterodistal section of mid- and hind trochanters with setae ( Fig. 7 , dotted oval) between primary setae ( Fig. 7 , arrows). Ventral trochanteral brush at distal section of each trochanter present on all legs (e.g., Fig. 7 dt). Proximal section of each trochanter of all legs with only one primary seta (e.g., Fig. 7 pt). Rows of minute spines present along ventral edges of femora; pairs of ventral-edge setae pale on forefemora ( Fig. 5 ), but dark on mid- and hind femora ( Fig. 6, 8 ). Tibiae of all legs with 2 pale, subapical spurs, tarsi with 2 long subapical setae; tarsal claws long, slender, curved, each with stout basal spine ( Figs 5–6, 8 ).

Abdomen. Abdominal segment I unsclerotized, whitish, with 1 dorsal ( Figs 4 , 9 dp) and 2 lateral fleshy protuberances ( Figs 4 , 9 lp). Dorsal sa 1, sa 2, and sa 3 (sensu Wiggins 1996) with 5–7 setae each, approximately one-third of them with medium brown basal sclerites; without setae posterior to dorsal protuberance ( Fig. 4 ). Lateral protuberances lacking posterior sclerites and each with single ventral seta ( Fig. 9 lp). Setae lacking posterior to dorsal protuberance ( Fig. 4 ). Abdominal sternum I with 5–7 setae in each sa 1, 9–14 setae in each sa 2, and 5–6 setae in each sa 3, situated ventral of lateral protuberances; about one-third of them with medium-sized, brown basal sclerites widely separated from each other ( Fig. 10 ). Anterior gills each consisting of three filaments, decreasing to 1–2 filaments on posterior segments. Dorsal gills present at most from segment II (postsegmental position) to segment V (presegmental position). Ventral gills ranging from segment II (presegmental) to segment VII (postegmental). Lateral gills present only on segment II (presegmental). Lateral fringe extending from anterior border of abdominal segment III ( Fig. 9 lf) to end of abdominal segment VIII. With large oval chloride epithelia on abdominal sterna II–VII ( Fig. 10 ce). Abdominal segments III–VII with 3–5 forked lamellae immediately dorsal of lateral fringe ( Fig. 11 fl). Number of posterodorsal setae on abdominal segment VIII typically 12, with 6 long and remainder short ( Fig. 13 pds); with 1 posterolateral seta ( Fig. 13 pls) and 2 tiny ventral setae present on each half ( Fig. 13 ). Abdominal tergite IX semicircular, brown, with darker muscle attachment spots ( Fig. 12 ); its posterior border with 4 long and 5 shorter setae, 1 of these shorter setae having position of central intermediate seta ( Fig. 12 , arrow); setae between inner- and outermost setae ( Fig. 12 is, os) shorter than 50% length of inner- and outermost seta. Anal prolegs of limnephilid type, yellowish brown, with dark brown muscle attachment spots ( Fig. 13 ). Lateral sclerites ( Fig. 13 ls) each with 7–9 dark dorsal setae and row of 5 dark ventral setae, 4 of latter very strong and prominent. Ventral sole plates ( Fig. 13 vs) yellow, each with black dorsal stripe and single anterior seta. Anal claw basal sclerites ( Fig. 13 ac) yellow, each with 4 short pale ventral setae and 3 longer, dark dorsal setae; anal claws dark brown, each with 1 small dorsal accessory hook ( Fig. 13 ac).

Case. Fifth instar larval case 14.9–18.1 mm long (n = 4), straight, slightly tapering posteriorly (width at anterior opening 3.8–4.9 mm and at posterior opening 3.0– 3.7 mm) ( Fig. 14 ), consisting of mixed mineral particles, plant fragments, and aquatic mollusc shells, both empty and including the gastropod’s soft body.

Figures

FIGURES 1–5. Limnephilus minos Malicky 1970, 5th instar larva. 1, head, frontal (a = antenna; small white numbers = setal positions; dotted oval = group of labral setae #1–4; white circle = alveolus of missing seta #17; arrow = terminal teeth of left mandible); 2, head and prosternum, ventral (c = cardo; cs = central prosternite; ls = lateral prosternite; ph = prosternal horn; va = ventral apotome; small white numbers = setal positions; white circle = alveolus of missing seta #18); 3, head, pro- and mesothoraces, right lateral (eps = episternum; epm = epimeron; ph = prosternal horn; arrow = transverse rim); 4, pro-, meso-, and metanota and abdominal tergum I, dorsal (dp = dorsal protuberance on abdominal tergum I; lp = lateral protuberance on abdominal segment I; ms = mesonotum; mt = metanotum; p = pronotum; sa1–3 = setal areas 1–3); 5, right foreleg, anterior face. Scale bars: 0.5 mm.

FIGURES 6–12. Limnephilus minos Malicky 1970, 5th instar larva. 6, right midleg, anterior face (arrow = proximodorsal seta); 7, detail of right midleg trochanter, anterior view (pt = proximal section of trochanter; dt = distal section of trochanter; arrows = proximal and distal primary setae; dotted oval = additional proximodorsal setae); 8, right hind leg, anterior face; 9, abdominal segments I–III, right lateral (dp = dorsal protuberance; lp = lateral protuberance; lf = lateral fringe); 10, abdominal sterna I–II, ventral (dotted ovals refer to sa1–3 = setal areas 1–3 on sternum I; ce = chloride epithelium); 11, forked lamellae of abdominal segment IV, right lateral (small numbers indicate lamellae #1 and 4; fl = forked lamellae; lf = lateral fringe); 12, abdominal terga IX–X, dorsal (arrow = one central intermediate ‘c’ seta on abdominal tergum IX; is = innermost seta; os = outermost seta). Scale bars: 0.5 mm.

FIGURES 13–16. Mesophylax and Limnephilus spp., 5th instar larvae. Figures 13–14. Limnephilus minos Malicky 1970: 13, tip of abdomen, right lateral (ac = anal claw; ls = lateral sclerite; pds = posterodorsal setae; pls = posterolateral seta; vs = ventral sole plate); 14, larval cases, right lateral. Figures 15–16. Mesophylax impunctatus aduncus (Navás 1923): 15, head, right frontolateral (a = antenna; small white numbers = setal positions; ph = prosternal horn; arrow = right mandible without terminal teeth); 16, head, ventral (c = cardo; va = ventral apotome; small white numbers = setal positions). Scale bars: 0.5 mm.