Rhyacophila hartigi Malicky 1971

Waringer, Johann & Malicky, Hans, 2020, The larva of Rhyacophila hartigi Malicky 1971, including a discriminatory matrix to the Italian Rhyacophila larvae with tufted multifilament gills (Rhyacophilidae, Trichoptera), Zootaxa 4731 (1), pp. 103-114 : 104-108

Description of the final instar larva of Rhyacophila hartigi Malicky 1971

Biometry. Body length 18.7 mm, head width 1.22 mm (n = 1). Chaetotaxonomy according to Williams & Wiggins (1981), anal proleg terminology following Nielsen (1942).

Head. Head capsule convergent anteriorly, maximum head width at level of posterior apex of frontoclypeal apotome ( Figs. 1–2 ). Coloration pale straw, with medium brown, oval muscle attachment spots at dorsal and lateral sides of parietalia, on frontoclypeal apotome, and along coronal suture ( Figs. 1–3 ). With median brown pigmented areas (1) on posterior third of frontoclypeal apotome confined to area ranging from posterior apex to level of setae #6 and including a semicircular row of 5 dark muscle attachment spots; in addition, with small, pale brown patches around pretentorial pits marked by setae #5; (2) on parietalia, dorsally from posterior frontoclypeal suture and converging to coronal suture ( Fig. 1 ); and (3) laterally, at eye level, from seta #12 to apophysis of foramen occipitale ( Fig. 3 ). Anterior border of head capsule medium to dark brown ( Figs. 1–2 ). Ventrally, posteromedian borders of parietalia reinforced by drop-shaped, heavily sclerotized areas ( Fig. 2 ). Frontoclypeal apotome bell-shaped, with deep central constriction ( Fig. 1 ). On each parietal, 12 dorsal (setae #1, 7, 9, 12–17, and 19–21) and 2 ventral (setae #8 and 18) primary setae present, some of them visible and marked in Figs. 1–3 . Frontoclypeal apotome with 5 pairs of primary setae, 2 of them near anterior border ( Fig. 1 ); in addition, with one single and three paired sensory pits. Tiny antennae situated between anterior border of eye and lateral mandible base, consisting of conical base and short apical flagellum. Labrum sclerotized, pale straw-coloured, with 6 pairs of primary setae; anteclypeus without longitudinal stripes ( Fig. 1 ) which are present in some other Rhyacophila species (e.g., R. polonica McLachlan 1879 ). Dark brown ventral apotome triangular, its anterior section heavily sclerotized, concave and semicircular, with rounded edges; its posterior section triangular ( Fig. 2 ). Mandibles dark brown, each with apical tooth ( Fig. 4 at) almost black; mandibles asymmetrical: right mandible with short, stout basal tooth ( Fig. 4 bt), this tooth lacking on left mandible and replaced there by straight cutting edge ( Fig. 4 ce); each mandible base with 2 setae laterally ( Fig. 4 , arrows).

Thorax. Pronotal sclerites large, covering pronotum totally; sclerites tapering posteriorly, thereby creating lateral constrictions with associated tiny dorsal bulges at approximately two thirds of pronotal length ( Fig. 5 , arrow). Pronotal sclerites brownish yellow, with whitish muscle attachment spots creating arc–like patterns posterolaterally, with pair of setae #5 near anterior borders of arc ( Fig. 5 ). Large, pale round spot around setal position #2; further pale muscle attachment spots creating arcs aiming at anterolateral pronotal corners at setal positions #22, 23 ( Figs. 3 , 5 ). Posterolateral edges of pronotal sclerites prolonged ventrally, with black posterior pronotal band interrupted by yellow patch ( Figs. 3 , 5 ). Lateral borders slightly concave and darkly striped, including anterolateral corners ( Fig. 3 ). Pronotal notch at anterolateral corner large, with 2 long setae ( Fig. 3 , #22, #23). Prosternal horn lacking, prosternite inconspicuous. Meso- and metathoraces totally unsclerotized, creamy, with purplish-blue-coloured areas subdivided by near-white bands (coloration may be modified by long preservation); each with single pair of anterior sa 1 setae and groups of one long and two tiny posterior sa 2 setae. Foretrochantins ( Fig. 3 tr) triangular, with black edges, each with anterior corners elongated into digitiform process bearing terminal seta #10. ( Figs. 3 , 6 ). Dorsal apex of pleural suture ( Fig. 3 ps) close to posterolateral prolongations of pronotum; proepisternum ( Fig. 3 es) small, quadrangular, yellowish brown; proepimeron ( Fig. 3 em) forming very narrow, black ventral plate below pleural suture. Episterna and epimera of meso- and metathoraces almost completely reduced to black vertical pleural sutures ( Fig. 8 ). Propleura without gills, pleura of meso- and metathoraces each with tufted gills originating from truncate base, splitting apically into dorsal and ventral branches, each bearing numerous gill filaments ( Figs. 7, 8 tg). Legs yellowish brown, with borders of sclerites darker and with numerous setae on coxae, trochanters, and femora; tibiae and tarsi with only small number of setae (some setae numbered in Fig. 6 ). Forefemora distinctly wider than mid- and hind femora; tarsal claws sickle-shaped, pointed, each with basal spur originating from conical base ( Figs. 6–8 ).

Abdomen. Abdomen dorsally purplish–blue, with coloured areas subdivided by pale bands, cream white ventrally (coloration may be modified by long preservation). Each segment with 2 pairs of dorsal primary setae (dislodged and missing from Fig. 9 ), with pair of tufted lateral gills matching morphology of gills on thoracic segments ( Fig. 9 tg), and pair of ventral setae ( Fig. 9 , #10). Lateral fringe lacking. Tergal sclerite of abdominal segment IX brownish yellow, quadrangular, with broad black anterior and posterior borders narrow or missing mesally ( Figs. 10, 11 ); setae #2 and 3 short, outer posterior border setae #4 long and distinct; lateral setae #5 each on small separate sclerite ( Figs. 10, 11 ). Anal proleg sclerites light brown, with dark brown borders and dark brown suture between anterior and posterior parts of proximal sclerite ’b’ ( Fig. 10 pb). Each proleg consisting of bipartite proximal sclerite ’b’ ( Fig. 10 pb) with oblique dark bar of suture extending onto strong basoventral hook ( Fig. 10 h ) anteriorly and with long terminal sword process ( Fig. 10 sp) posterodorsally; distal sclerite ’b’ also with dorsal hornlike process with blunt tip ( Figs. 10, 11 bd); ventral sclerite ‘c’ rectangular, with pointed dorsal outline ( Fig. 10 c ); narrow ventral sclerite ( Fig. 10 bv) with long median seta; anal claw ( Fig. 10 ac) partially divided by ventral membrane into proximal and distal sections, proximal section with one apicoventral tooth, distal section fitted with two basoventral teeth ( Fig. 10 , arrow); anal claw teeth obliquely angled relative to longitudinal axis of anal claw; distal anal-claw tooth length ( Fig. 12 dtl) subequal to anal-claw width at distal tooth insertion ( Fig. 12 cw).

Morphological diagnosis to separate fifth instar larvae of Rhyacophila hartigi from those of other European Trichoptera

A summary of morphological features for the identification of European caddisfly families was given by Waringer & Graf (2013). Within the framework of the key by Waringer & Graf (2011), R. hartigi (and other Rhyacophila species with tufted gills) is separable from other species by possessing the following features:

- Only pronotum sclerotised ( Figs. 3 , 5 );

- Labrum sclerotized ( Fig. 1 );

- Abdominal segment IX with dorsal sclerite ( Fig. 11 );

- Without transportable case;

- With tufted gills on meso- and metathorax as well as on abdominal segments ( Figs. 7–9 ).

Further, a morphomatrix can be used to separate larvae of the Italian Rhyacophila species with tufted gills known so far. Species can be separated by morphological differences located on anal prolegs and by details of head and pronotum coloration summarized in Table 1 .

Figures

FIGURES 1–3. Rhyacophila hartigi Malicky 1971, 5th instar larva. 1, head, dorsal (lb = labrum; small numbers refer to setal positions); 2, head, ventral (va = ventral apotome; small numbers refer to setal positions); 3, head and prothorax, right lateral (em = epimeron; es = episternum; pr = pronotal sclerite; ps = pleural suture; tr = trochantin; small numbers refer to setal positions). Scale bars: 0.5 mm.

FIGURES 4–8. Rhyacophila hartigi Malicky 1971, 5th instar larva. 4, mandibles, ventral (at = apical tooth; bt = basal tooth; ce = cutting edge; lm = left mandible; rm = right mandible; arrows = lateral setae); 5, prothorax, dorsal (small numbers refer to setal positions; dotted oval = tiny setae of pronotal notch; arrow = posterolateral constriction with dorsal bulge); 6, right foreleg, anterior (small numbers refer to setal positions); 7, right midleg, anterior (tg = tufted mesothoracic gill); 8, right hind leg, anterior (tg = tufted metathoracic gill). Scale bars: 0.5 mm.

FIGURES 9–15. Figures 9–12. Rhyacophila hartigi Malicky 1971, 5th instar larva. 9, abdominal segments IV and V, left lateral (tg = tufted abdominal gills; small numbers refer to setal positions);10, abdominal segments IX, X and anal proleg, right ventrolateral (ac = anal claw; bd = distal ‘b’ sclerite; bv = ventral ‘b’ sclerite; c = ‘c’ sclerite; h = proximal hook of sclerite ‘b’; pb = proximal ‘b’ sclerite; sp = sword process; small numbers refer to setal positions; arrow = distal tooth on anal claw); 11, abdominal segments IX, X and anal proleg, dorsal (bd = distal ‘b’ sclerite; pb = proximal ‘b’ sclerite; sp = sword process; small numbers refer to setal positions); 12, detail of right anal claw (cw = claw width; dtl = distal tooth length; sp = sword process; small numbers refer to setal positions; white double-headed arrows = dimensions of claw width and distal tooth length; dash line = insertions of ventral teeth on anal claw). Figures 13–15. Rhyacophila spp., 5th instar larvae, details of right anal claw. 13, R. aurata Brauer 1857 (cw = claw width; dtl = distal tooth length; white double-headed arrows = dimensions of claw width and distal tooth length); 14, R. foliacea Moretti 1981 (redrawn from Moretti 1983); 15, R. simulatrix simulatrix McLachlan 1879. Scale bars: 0.5 mm.