Drusus medianus, Marinkovic-Gospodnetic, 1976

Posilović, Hrvoje, 2010, Description of the larvae of Drusus ramae Marinković- Gospodnetić and Drusus medianus Marinković- Gospodnetić (Trichoptera: Limnephilidae) with some genetic, distributional, ecological, faunal and conservation notes, Zootaxa 2484, pp. 1-24 : 8-12

Description of fifth instar larva of Drusus medianus

Case and Larva

Case constructed completely of mineral particles ( Fig. 16 ), slightly curving, total length 9.98–12.55 mm, width of anterior part 2.42–3.16 mm, width of posterior part 1.72–2.16 mm (n=20). Overall body shape eruciform ( Fig. 17 ), total length without case 10.17–11.06 mm (n=20).

Head

Head capsule hypognathous, ellipsoidal, with width 1.37–1.48 mm (n=20) ( Figs 17–18 , 22 ). Head brown, dorsally darker and laterally lighter ( Figs 16–17 ), with granular surface sculpturing surface ( Fig. 19 ). Genae of the parietals reddish-brown to yellow with lighter ring around each eye ( Fig. 18 ). Posterior part of dorsum with numerous, dark muscle attachment spots. Distinct area of spinules (small spines, size approximately 0.015–0.025 mm) positioned laterally on each side of head capsule next to the eye ( Figs 20–21 ). Spinules also in some specimens on posterior part of each antennal prominence. Frontoclypeal apotome bell-shaped with narrow central region ( Fig. 22 ). Antennae short, brown to dark brown, each positioned on small, noticeable prominences accompanied by 2 prominent lateral setae (setae no. 7 and no. 9) ( Figs. 18–19 ). Other primary setae positioned as shown in Fig. 22 and light or dark and short or long as described for D. ramae .

Labrum symmetrical, brown posteriorly to yellowish anteriorly, with setal brush at anterolateral margins and 5 pairs of thin primary setae on dorsal surface.

Mandibles black, mesal part reddish. Typical for grazers, mesal margin with setal brush and without teeth except 1 small tooth usually present subapically ( Fig. 23 ). Two setae present laterobasally on each mandible ( Fig. 23 ).

Labium and maxillae light-brown (yellowish). Maxillary palps 5-segmented.

Thorax

Pronotum dark brown to black ( Figs 16–18 ) with granular surface sculpturing ( Figs 24–25 ). Posterior margin rounded, both posterior and lateral margins thick and darkly sclerotized ( Fig. 18 ). Anterior part (i.e. 50–60 %) of pronotum slightly concave, posterior part with a prominent median hump ( Figs 18 , 24 ). Pronotum bearing dark setae, especially laterally and on anterior margin, some of them long and conspicuous ( Figs 18 , 24 ). Dorsal and lateral regions of pronotum covered with numerous white recumbent setae ( Figs 24- 25 ). Prosternal horn present.

Mesonotum sclerites brown, lighter than pronotum, with dark muscle attachment spots and uneven (rugged) surface. Long, dark setae at positions sa 1, sa 2 and sa 3 ( Fig. 26 ). Posterior and lateral margins thick and darkly sclerotized.

Metanotum with 3 pairs of dorsal sclerites ( Fig. 26 ). Anteromedian (sa 1) sclerites ellipsoid, with distance between them smaller than their length ( Figs 26 , 48–49 ), covered by setae, mainly anteromedially, color similar to mesonotum. Posteromedian (sa 2) sclerites smaller and lighter than sa 1 sclerites ( Figs 26 , 48–49 ), diagonally and irregularly ellipsoid and with many dark setae. Group of setae present on membranes between sa 2 sclerites and between sa 2 and sa 3 sclerites. Lateral (sa 3) sclerites longitudinally prolonged, sickleshaped, lighter brown with dark median region, and group of setae anteriorly ( Fig. 26 ).

Legs yellow-brown to dark brown or black, with dark ventral and dorsal margins ( Figs 16–18 ). Foreleg coxae with dark setae on ventral and dorsal edges. Foreleg trochanters without dorsal setae, each with few light-yellow setae on ventral margin and distally with dense ros of short, fine, yellowish setae (trochanteral brush) continuing onto basoventral margin of femur ( Fig. 27 ). Foreleg femora each with dark setae on dorsal edge, few stout, light-yellow setae on ventral margin in addition to basoventral dense row of short, fine, yellowish setae ( Fig. 27 ). Mid- and hind leg coxae and femora with dark setae on both ventral and dorsal edges, midleg trochanters with few, fine, yellowish setae apicoventrally ( Figs 28–29 ). Additional setae present on anterior and posterior faces of all femora. Setae on dorsal edges of tibiae present only distally in all legs. Tarsae each with claw and basal seta, and tibial spurs light brown, almost yellowish. Foreleg coxae and femora wide compared to those of mid- and hind legs ( Figs 27–29 ). Mid- and hind-legs similar in shape and size ( Figs 28–29 ), with slender coxae, trochanters, and femora.

Abdomen

Abdominal segment I with well-developed dorsal and lateral humps (protuberances). Numerous setae present anterior and lateral to dorsal hump. It is not possible to distinguish between setal areas sa 1 and sa 2 on dorsal side. With numerous ventral setae, some of them with small sclerites at bases. Lateral humps with few setae.

Single filamentous gills ( Fig. 17 ) present on segments II–VII ( Fig. 30 ). Dorsal pre- and post-segmental gills present on segments II–VI; ventral pre- and post-segmental gills present on segments II–VII. Lateral presegmental gills present on segments III–IV and lateral post-segmental gills on segments II–IV ( Fig. 30 ). In some specimens dorsal pre-segmental gills on segment VI, post-segmental gills on segments V and VI, and lateral pre- and post-segmental gills on segment IV are not present ( Fig. 30 ). Number of dorsal setae on abdominal segment VIII varies (2–6). Lateral fringe extends from last third of segment II to first half of segment VIII; in some specimens, only few setae forming lateral fringe on segment II or setae not visible.

Segment IX bearing irregular, semicircular, light brown dorsal sclerite, generally with 8 long, dark setae on posterior margin and several shorter, light setae on posterior half of sclerite ( Fig. 31 ). Anal prolegs typical of limnephilids ( Fig. 32 ), each with lateral sclerite longitudinally prolonged, sickle-shaped, yellowish, with small setae scattered over posterior 2/3rds and 2 large, dark setae at posterior end ( Fig. 32 ). Anal claws brown.

Figures

FIGURES 16 – 21. Drusus medianus Marinković- Gospodnetić, 1976. 16, larva in its case, right lateral view; 17, larva, right lateral view; 18, head, pronotum and mesonotum, right lateral view; 19, head with spinules above eye, right lateral view; 20, area with spinules, right lateral view; 21, spinules, right lateral view.

FIGURES 22 – 26. Drusus medianus Marinković- Gospodnetić, 1976. 22, head, frontal view; 23, right mandible, dorsal view; 24, pronotum, right lateral view; 25, white recumbent setae on posterior part of pronotum, right lateral view; 26, thorax (pronotum, mesonotum and metanotum), dorsal view.

FIGURES 46 – 53. Metanota of Drusus spp., showing anteromedian (sa 1) and posteromedian (sa 2) sclerites. 46 – 47, Drusus ramae Marinković- Gospodnetić, 1976; 48 – 49, Drusus medianus Marinković- Gospodnetić, 1971; 50 – 51, D. radovanovici septentrionis Marinković- Gospodnetić, 1976; 52 – 53, Drusus croaticus Marinković- Gospodnetić, 1971.

FIGURES 27 – 32. Drusus medianus Marinković- Gospodnetić, 1976. 27, right foreleg, lateral view; 28, right mid-leg, lateral view; 29, right hind-leg, lateral view; 30, gill diagram: position of filaments on left side of abdominal segments I – VIII, ●, gills always present, O, gills not always present; 31, abdominal segment IX, dorsal view; 32, anal proleg, left lateral view.