Rhyacophila meyeri

Waringer, Johann, Vitecek, Simon & Graf, Wolfram, 2016, Larval morphology and identification of Rhyacophila meyeri McLachlan 1879 (Trichoptera: Rhyacophilidae), Zootaxa 4093 (4), pp. 559-565 : 560-563

Description of the fifth instar larva of Rhyacophila meyeri

Morphological terminology after Wiggins (1998).

Biometry. Body length of final instar larva ranging from 9.5 to 11.2 mm, head width from 0.55 to 0.68 mm (n= 4).

Head. Head capsule prognathous, elongated, with smooth surface and maximum width at head center ( Fig. 1 ). Dorsal and ventral head sections chestnut brown, with pale muscle attachment spots on frontoclypeus and brown ones on parietals ( Figs. 1–2 ). With paler areas around eyes, along lateral sections of parietals and ventral of occipital margin ( Figs. 1–3 ). Head capsule with complete set of primary setae (5 pairs on frontoclypeus, 11 pairs on parietals), with setae # 6, 7, 9 and 14 long and conspicuous. In addition, 13 pairs of sensory pits (sensilla campaniformia) are present, 4 pairs of them situated on frontocylpeus. Frontoclypeus bell-shaped, with deep central constriction posterior of eye level and with bulge within posterior third ( Fig. 1 ). Antennae near anterior parietal border, extremely small. Sclerotized labrum semicircular, yellowish brown with pale anterior border ( Fig. 1 ). Submentum dark brown, triangular, distinctly wider than long ( Fig. 2 ). Mandibles medium brown, almost black centrally, and asymmetrical ( Figs. 4, 5 ): in dorsal view, left mandible with short, stout basal tooth (lacking on right mandible and replaced there by straight cutting edge). Both mandibles with apical and subapical teeth, distinctly larger on right mandible. Hairy brush in central concavity lacking. Each mandible base with one very short and one large dark seta ( Fig. 5 ).

Thorax. Pronotum fully covered by 2 large sclerites, tapering posteriorly, wider than head capsule; pronotal sclerites chestnut brown, slightly lighter in colour laterally, with black or brown muscle attachment spots creating arc-like patterns, their arms (1) meeting centrally, (2) pointing towards anterolateral corners and (3) pointing towards posterior border ( Figs. 1, 3 ). Posterior pronotal corners slightly prolonged ventrally. Posterior and lateral margins thickened and darkly striped, including anterolateral corners. Pronotal notch at anterolateral corner large, deep and semicircular, with one large and two smaller setae. Up to 10 setae in each anterolateral group surrounding pronotal notch. Anterior borders of pronotal sclerites with dense fringe of very short, curved, fine, yellow setae and 2 long primary setae ( Fig. 6 , dotted oval). In addition, 7 setae of varying lengths distributed over central section of each pronotal half. Prosternal horn lacking.

Mesothorax dark purplish-brown to purplish-blue with coloured areas subdivided by whitish bands ( Fig. 11 ). Mesonotum largely unsclerotized except small roundish sclerotized plate at dorsal posterior center ( Fig. 11 , dotted oval). Metathorax same colour, completely unsclerotized. Foretrochantin large, with dark central stripe and large rounded anterior process ( Fig. 3 ). Mid- and hind trochantin smaller, elongated, with blackish ventral margin.

Legs pale brown, with numerous setae on coxae, trochanters and femora; tibiae and tarsi with only small number of setae (Figs. 8–10). Forefemora distinctly wider than mid- and hind femora. Each tibia with 2 long, brown, slender apical spurs. Tarsal claws long and slender, curved, pointed, with basal spur (Figs. 8–10).

Abdomen. Abdomen slightly flattened dorsoventrally; dorsally dark purplish-brown to purplish-blue, with coloured areas subdivided by whitish bands. Laterally and ventrally creamish white ( Fig. 11 ). Gills and lateral fringe lacking.

Abdominal dorsum IX with large, yellow quadrangular sclerite with medium brown band along anterior border ( Fig. 12 s). Anal proleg lateral sclerite without curved spike, but with freely projecting ventral hook. Anal claw long, regularly curved, partially divided by ventral membranous section and fitted with 2–3 ventral teeth ( Fig. 12 , arrow).

Morphological separation of fifth instar larvae of Rhyacophila meyeri McLachlan 1879 from other European Trichoptera

A summary of morphological features for the identification of Rhyacophilidae larvae was provided by Buholzer (1978), Coppa et al. (2012), Edington & Hildrew (1995), Graf (1993), Viera-Lanero (2000), and Waringer & Graf (2011, 2013). Within the framework of the above Rhyacophilidae keys, the genus Rhyacophila is separable from other caddis larvae by the following combination of characters:

- pronotum completely sclerotized, meso- and metanotum unsclerotized except a tiny dorsal sclerite which is

present in some Rhyacophila species at the center of the posterior mesonotal border ( Figs. 1 , 11 ); - without transportable case;

- prosternal horn lacking;

- labrum sclerotized ( Figs. 1, 2 );

- abdominal segment IX with dorsal sclerite ( Fig. 12 s);

Within the genus Rhyacophila , gill filaments are completely lacking in larvae of R. meyeri ( Fig. 11 ) as in other species of the Hyporhyacophila group for which larvae have been described ( Rhyacophila glareosa , R. hirticornis , R. philopotamoides , R. stigmatica , R. aquitanica , R. pubescens , R. tristis ). Based on the presence of ventral teeth at the anal claw, R. meyeri keys together with R. glareosa , R. hirticornis , R. philopotamoides , and R. stigmatica . Within this group, the ventral side of the head capsule is pale in R. glareosa , R. hirticornis , and R. philopotamoides whereas it is dark in R. meyeri and R. stigmatica . The latter species pair can be separated morphologically by the fact that in R. meyeri , intermediate dark setae are lacking at the anterior pronotal border, and biometrically by the maximum head width of the last instar larvae which is 0.55–0.68 mm in R. meyeri but> 0.90 mm in R. stigmatica ( Table 1).

Figures

FIGURES 1 – 6. Rhyacophila meyeri McLachlan 1879, 5 th instar larva. 1, Head and pronotum, dorsal. 2, Head, ventral. 3, Head and pronotum, right lateral. 4, Mandibles, dorsal. 5, Mandibles, ventral. 6, Detail of anterior pronotal border, dorsal (dotted oval: only short, curved setae and few long primary setae present). FIGURE 7. Rhyacophila stigmatica (Kolenati 1859), 5 th instar larva. Detail of anterior pronotal border, dorsal (dotted oval: short, curved setae, widely-spaced intermediate and few long primary setae present). FIGURE 8. Rhyacophila meyeri McLachlan 1879, 5 th instar larva. Right foreleg, posterior face. Scale bars: 0.5 mm (except 3: 1 mm).

FIGURES 9 – 12. Rhyacophila meyeri McLachlan 1879, 5 th instar larva. 9, Right midleg, posterior face. 10, Right hind leg, posterior face. 11, Meso-, metanotum and anterior abdominal segments, dorsal (dotted oval: sclerite at mesonotum). 12, Tip of abdomen, right lateral (s = dorsal sclerite on abdominal segment IX; arrow: teeth on anal claw). 13, Sampling site (spring brook in Valchiusella near Traversella, Tissone, Italy; 1200 m above sea level). Scale bars: 0.5 mm (except 11: 1 mm).