Hydropsyche penicillata Martynov 1931

Ge, Xinyu, Wang, Yinchang, Wang, Beixin & Sun, Changhai, 2020, Descriptions of larvae of three species of Hydropsyche Pictet 1834 (Trichoptera Hydropsychidae) from China, Zootaxa 4858 (3), pp. 358-374 : 363-367

Hydropsyche penicillata Martynov 1931

General Description. Larvae (5th instar). The body grayish white in alcohol. Head and pronotum dark brown, legs and anal claws yellowish brown.

Head. Head ( Fig. 5A ) capsule subquadrate, nearly square, 1.5 mm long, 1.3 mm wide in dorsal view. Dorsum

of head overall coloration dark brown, with 3 yellow patches longitudinally arranged on frontoclypeal apotome in dorsal view; anterior patch largest and transversely elliptical, middle one drop-shaped, posterior one smallest and somewhat cucurbit-shaped. Anterior margin of frontoclypeal apotome nearly straight. Frontoclypeal apotome with conspicuously mediotransversal fold arm. Frontoclypeal apotome with posterior angle ogival, at an angle of about 80°, with posterior portion of each frontoclypeal suture slightly sinuous. In lateral view ( Fig. 5B ), eyes oval, black, each surrounded by conspicuous light-yellow mark. Yellowish stripe behind each eye extended to posterior margin of parietal and posterodorsally nearly to epicranial suture. In ventral view ( Figs 5C, 5E ), anterior ventral apotome nearly triangular, dark brown, with anterior border slightly concave and anterolateral angles rounded. Genae with large subrectangular yellow patch along one third of anterior ventral ecdysial line. Ventral ecdysial line more than twice as long as anterior ventral apotome. Posterior ventral apotome tiny, triangular, dark brown. Dorsum of head with brown hair-like setae, short dark-brown truncate peg-like setae, and short acuminate peg-like setae. Muscle scars lighter than background. Labrum dark brown, with its anterior margin convex and each anterior lateral margin with hair-like setae. Mandibles ( Fig. 5D ) brown, triangular in dorsal view, left mandible with two apical teeth and three subapicomesal teeth; with lateral margin having about eight setae and middle of inner side having brush of about dozen stiff hairs. Right and left mandibles symmetrical. Submentum ( Fig. 5E ) in ventral view with basal 2/3 somewhat trapezoidal and distal 1/3 divided, forming two lobes; posterior margin slightly convex; each anterolateral corner with some long, strong setae and many short setae. Maxillae ( Fig. 5E ) each with cardo approximatively rhomboid, dark brown. Stipes ( Fig. 5F ) with three clusters of setae, a cluster with about 12 setae on membranous portion of stipes, seven setae and five setae on lateral and medial portions of triangular sclerotized part of stipes, respectively. Maxillary palps each 5-segmented, galea adjacent to medial margin of palp. Labium ( Fig. 5F ) triangular and short with brown mentum in ventral view.

Thorax. Pronotum ( Fig. 6A ) subrectangular and dark brown in dorsal view, pronotum subdivided longitudinally by mesal suture, posterior margin black submesally. Pronotum covered with acuminate peg-like setae; short and dark-brown truncate peg-like setae; and slender, short, black hair-like setae. Prosternal plate large ( Fig. 6B ), nearly trapezoidal, with its width about 4 times its length; anterior margin blackish, slightly sinuous and slightly convex anteriorly on meson, posterior margin slightly concave. Intersegmental fold often covering two pairs of sclerites posterior of prosternal sclerite; on each side lateral and submesal sclerite pieces behind prosternal sclerite fused into subrhombic sclerites ( Fig. 6B ), each with posterolateral edge having broad triangular notch.

Mesonotum ( Fig. 6C ) dark brown in dorsal view, undivided on midline, with anterior margin straight, anterolateral angles and lateral margins and posterolateral angles black; pair of dark brown lines issuing from posterolateral angles extending anteromesad to level of ends of V-shaped black mark on middle of posterior margin, each line with anteromesal end bulging and darkened. Diagonal grooves indistinct. Sparse truncate peg-like setae scattered over whole surface of notum, anterior margin with many black hair-like setae and few truncate or acuminate peg-like setae.

Metanotum ( Fig. 6D ) of same color as mesonotum and undivided on midline, posterior margin shallowly concave, slightly sinuous black mark on middle of posterior margin, anterolateral angles and lateral margins black; broad and deep diagonal grooves issuing from anterolateral angles and more conspicuous than those of mesonotum extending 2/3 distance toward posterior meson of notum. Muscle scars darker than background, longitudinally arranged. Setae on mesonotum and metanotum less dense than those on pronotum. Mesosternum and metasternum with one and two pairs of single-stemmed ventral gills, respectively.

Legs. Legs ( Figs7A, 7C, 7D ) yellowish brown in alcohol. Forelegs slightly shorter and thicker in structure and darker in color than mid- and hind legs. Each foretrochantin bifurcate ( Fig. 7B ), two branches divergent at an angle of about 70º, with about 15 setae. Forecoxae shorter than mid- and hind coxae, and somewhat conical in lateral view. Dorsal margin with 15–20 spike-like setae. Trochanters each two-segmented and approximately triangular, each with basal segment subtriangular and shorter than subtriangular apical segment, trochanteral brush present mostly on apical segment, ventral margin with more than 30 spike-like setae and three long-slender setae.

Forefemora in lateral view pentagonal, each with dorsal margin (scraper) protruding at midlength; ventral and dorsal margins with dense long-slender setae and spike-like setae, respectively. Foretibiae and foretarsi tube-like stouter than mid- and hind tibiae and tarsi. Tarsal claw of foreleg slightly curved downwards, with basal seta small. Mid- and hind coxae cylindrical, with dense spike-like setae. Trochanters each two-segmented and approximate triangular with dense spike-like setae and some long-slender setae. Mid- and hind femora cylindrical, with 1–2 long-slender setae and shorter spike-like setae. Tarsal claws of mid- and hind legs each slightly curved downwards apically, with basal seta stout.

Abdomen. Abdominal segments I–IX covered densely with black hair-like setae and sparsely with half-erect scale-hair setae ( Fig. 7E ). Segment I with two pairs of bifid-stemmed gills; segments II–VI each with ventrolateral bifid-stemmed gill and ventromesal single-stemmed gill; segments III–VI lateral with pupal gill buds, abdominal segment VII with pair of ventral bifid-stemmed gills. Subtriangular sterna of segments VIII and IX each with pair of ventral plates ( Fig. 7F ), brown, covered with tapered, short acuminate peg-like setae, posterior borders of these sternites with some black long slender setae. Anal prolegs ( Fig. 7G ) each slightly sclerotized with spike-like setae and apical part with about 30 long slender setae arranged in one plane similar to spines of Chinese fan. Anal claws ( Fig. 7G ) yellowish brown, hook-like, angled about 100º.

Diagnosis. The larva of H. penicillata is very similar to the larva of H. columnata Martynov, 1931 ( Xu et al 2018) in the cephalic color patterns and the overall shape in dorsal view, but differs from it in that (1) the yellow mark on the posterior margin of the frontoclypeal apotome is somewhat cucurbit-like, not oval; (2) the cardo is sub-rectangular, not triangular; and (3) the posterior prosternal sclerites each has a triangular notch on the outside border, not an irregular notch. It is also similar to the larva of H. trifora Li & Tian, 1990 ( Xu et al 2018), but can be distinguished from the latter in that (1) in H. penicillata the genae have a rectangular yellow mark anteriorly with anterolateral angles produced, but in H. trifora the anterior margins of the genae are yellow; and (2) the prosternal plate width is about four times its length, not seven times as in H. trifora .

Material examined. Four larvae, CHINA, Si-chuan Province , Ping-shan County, Xin-shi Town , Xian-fengcun , Xi-ning He, 28°68’57”N, 103°76’61”E, Alt. 368 m, 13 Aug 2019, collected by Xin-yu Ge & Yin-chang Wang ; five larvae and three males, same location, 19 Nov 2019, collected by Xin-yu Ge & Xiao Chen ; six larvae 16 May 2019, same location, collected by Xin-yu Ge & Xiao Chen.

Notes. The larvae of H. penicillata were collected in Xi-ning He stream. The stream is 10–15 m wide and 0.2–0.4 m deep, with water transparency about 0.3 m. Filamentous green algae were rare, indicating the stream may be oligotrophic. The substrate of the stream consists of pebbles, cobble, and boulders. Lots of larval retreats were found under the stones, sometimes on the marginal areas of the stones near the substrate surface.

Figures

FIGURE 5. Head of Hydropsyche penicillata Martynov 1931. 5A, dorsal; 5B, right lateral; 5C, ventral; 5D, left mandible, dorsal; 5E, submentum cardo and anterior ventral apotome, ventral; 5F, maxillae and labium, ventral. Scale bars: 0.1 mm.

FIGURE 6. Thorax of Hydropsyche penicillata Martynov 1931. 6A, pronotum, dorsal; 6B, prosternal plates and posterior prosternal sclerites, ventral; 6C, mesonotum, dorsal; 6D, metanotum, dorsal. Scale bars: 0.1 mm.

FIGURE 7. Legs and abdomen of Hydropsyche penicillata Martynov 1931. 7A, right foreleg, right lateral; 7B, right propleuron, right lateral; 7C, right midleg, right lateral; 7D, right hind leg, right lateral; 7E, setae of abdominal tergum VII, left dorsolateral, dorsal; 7F, plates on abdominal sterna VIII and IX, ventral; 7G, anal prolegs, left lateral. Scale bars: 0.1 mm.