Drusus croaticus

Kučinić, Mladen, Previšić, Ana, Gottstein, Sanja, Hrašovec, Boris, Stanić-Koštroman, Svjetlana, Pernek, Milan & Delić, Antun, 2008, Description of the larvae of Drusus radovanovici septentrionis Marinković- Gospodnetić, 1976 and Drusus croaticus Marinković-Gospodnetić, 1971 (Trichoptera: Limnephilidae) from Bosnia and Herzegovina, and Croatia, Zootaxa 1783 (1), pp. 1-17 : 7-9

Description of the fifth instar larva of Drusus croaticus

Larva. Case slightly curved, constructed completely of mineral particles, ( Fig.18 ); length 9.16-12.89 mm (N = 35) (Bijela rijeka River), 13.05-17.03 mm (N=15) (Kostelka River). Larval body shape eruciform ( Fig. 19 ); body length 10.47-13.70 mm (N = 35) (Bijela rijeka River), 11.96-14.73 mm (N=15) (Kostelka River).

Head. Head capsule width 1.66-1.87 mm (N=35) (Bijela rijeka River) and 1.72-1.84 mm (N=15) (Kostelka River); ellipsoid in shape and hypognathous ( Figs. 19, 20, 21 ). Head brown to black, darker dorsally and lighter laterally ( Figs. 18, 19, 20 ), with granular sculpturing surface ( Fig. 20 ). Posterior part of dorsum with numerous, dark muscle attachment spots. Genae of parietals reddish-brown to yellow with lighter ring around eyes ( Fig. 20 ). Frontoclypeal apoptome bell-shaped, with narrow central region like in most Limnephilidae ( Fig. 22 ). Antennae short, dark brown to black, positioned on small, noticeable prominences, with 1 prominent seta at each side (setae no. 7 and no. 9) ( Figs. 21, 22 ).

Head with only few setae, mainly positioned at marginal regions ( Figs. 20, 21, 22 ). Three prominent setae present at lateral margin, 6 setae present on anterior margin of head (setae no. 1, no. 2 and no. 3). Dorsal margin of head without prominent setae; on each side of coronal suture one short, light setae (setae no. 17). One pair of light and short setae laterally of posterior region of frontoclypeal apoptome (setae no. 6), one pair of long and black setae at central region of frontoclypeal apoptome (setae no. 5), and one pair of long and light setae laterally of anterior region of frontoclypeal apoptome (setae no. 4); 2 light setae present on the ring encircling eye.

Labrum symmetrical, brown to reddish-brown, with setal brush at anterolateral margins and few short, pronounced setae on dorsal surface. Mandibles black, without teeth along edges and with median setal brush ( Fig. 23 ). Two setae present laterobasally on mandibles ( Fig. 23 ). Labium and maxillae light-brown. Brown submental sclerites on labium, each with one prominent, dark seta. Maxillary palps five-segmented. Ventral apoptome brown, bell shaped with pointed apex ( Fig. 24 ).

Thorax. Pronotum dark brown to black, with granular sculpturing surface ( Fig. 20 ). Posterior margin rounded, both posterior and lateral margins thick and darkly sclerotized ( Fig. 20 ).

Pronotum of same colour as head; in lateral view anterior two-thirds flat, posterior one-third (about last third of pronotum) curving to grooved posterior margin (slope of curve around 45°), posterior part with median, weak pit ( Figs. 20 , 25 ). Posterior margin thick and grooved. Mid-dorsal ecdysial line visible as thin, light-colored line contrasting darker pronotal surface. Setae present in large numbers only on lateral sides of pronotum ( Fig. 25 ). Prosternal horn present.

Mesonotum sclerites brown to dark brown, generally lighter than pronotum with dark muscle attachment spots, surface rugged; long, dark setae in positions sa1, sa2 and sa3 ( Fig. 26 ). Posterior and lateral margins thick and darkly sclerotized ( Fig. 25 ).

Metanotum with three pairs of metadorsal sclerites ( Fig. 26 ). Anterior-median sclerites ellipsoid, distance between sclerites smaller than sclerite lengths ( Fig. 26 ). Covered by setae, mainly at median area of anterior margin; surface colour similar to that of mesonotum. Posterior sclerites smaller than anterior sclerites, ellipsoid, with many setae ( Fig. 26 ). Group of setae present between posterior sclerites and between posterior and lateral sclerites. Lateral sclerites prolonged, sickle-shaped, lighter brown with dark median region and group of setae on anterior region ( Fig. 26 ).

Legs light brown to brown with black ventral and dorsal margins. Numerous setae on coxa, trochanter and femur; small number of setae on tibia and tarsus ( Figs. 27, 28, 29 ). Tarsal claws and their basal setae, and tibial spurs of each leg brown, light brown or yellowish. Forleg coxa and femur ( Fig. 27 ) wide compared to mid- ( Fig. 28 ) and hind-legs ( Fig. 29 ). Foreleg trochanter and femur with few yellow, short, stout, setae (spurs) at the ventral margin; row of thin, yellow setae on ventral margin on distal part of trochanter (trochanteral bursh). Mid- and hind-legs of similar shape and size; coxa and femur slender ( Figs. 28, 29 ). Distoventral margin of mid-legs with trochanter carrying few thin, yellowish setae. Hind-leg coxa and femur slender, without yellow, thin setae on ventral margin of trochanter.

Abdomen. Abdominal segment I with well developed dorsal hump pair of lateral humps ( Fig. 26 ). Numerous setae present anteriorly and laterally of dorsal hump ( Fig. 26 ); setal areas sa1 and sa2 indistinguishable ( Fig. 26 ). Numerous setae present on ventral side; four setae with small sclerites at bases; small number of setae present on lateral hump.

Single filamentous gills ( Fig. 19 ) present on segments II-VII ( Fig. 33 ). Dorsal pre-segmental gills present on segments II-VII; dorsal post-segmental gills present on segments II-VI. Ventral pre- and post-segmental gills present on segments II-VII and lateral pre- and post-segmental gills present on segments II-IV. Variability in gills presence observed in 20-30 % of specimens. In some specimens dorsal post-segmental gills are present on segment VII, lateral pre-segmental gills are present on segment V, and lateral pre-segmental gills are present on segment II ( Fig. 33 ). Lateral fringe extending from posterior one-third of segment II to end of segment VIII.

Segment IX with irregular, semicircular dorsal light brown sclerite, with several distinct setae (8 of them prominent) at posterior margin ( Fig. 30 ). Anal prolegs typical limnephilid-type ( Fig. 30 ). Lateral sclerite prolonged, sickle-shaped, yellowish with small setae mainly in posterior region ( Fig. 31 ). Anal claws brown to dark-brown.

Figures

FIGURES 18–24. Drusus croaticus Marinković-Gospodnetić, 1971. 18, larva in its case, lateral view; 19, larva, lateral view; 20, head and pronotum, dorsolateral view; 21, head lateral view; 22, head capsule, frontal view; 23, mandibles, dorsal view; 24, head capsule, ventral view.

FIGURES 25–31. Drusus croaticus Marinković-Gospodnetić, 1971. 25, pronotum, mesonotum, lateral view; 26, pronotum, mesonotum and metanotum, dorsal view; 27, forelegs, lateral view; 28, mid-legs, lateral view; 29, hind-legs, lateral view; 30, abdominal segment IX, dorsal view; 31, anal proleg, lateral view.

FIGURES 32–33. Gill diagrams: position of filaments on abdominal segments I–VIII; —gills always present; ☺— gills not present always. 32, Drusus radovanovici septentrionis Marinković-Gospodnetić, 1976; 33, Drusus croaticus Marinković-Gospodnetić, 1971.