Male strongly micropterous; female macropterous. Process of male tergite 9 projecting headward (Figs. 1–4, 7–8). Main epiproct sclerite slender, smoothly truncated and with a slightly blunted tip in lateral view (Figs. 2–3). Main epiproct sclerite with a small “hunchback” dorsally in its middle section (Figs. 3–4).

Head, thorax, appendages and basal segments of the abdomen as typical for the genus. Male strongly micropterous (Fig. 9). Female macropterous. Body length: holotype 5.0 mm, male paratypes 4.9–7.5 mm, female paratypes 9.0–10.1 mm; forewing length of males: holotype 1.1 mm, male paratypes 0.5–1.8 mm, female paratypes 10.0–11.0 mm.

Males (Figs. 1–10). Process of tergite 9 highly elevated and projecting headward, in lateral (Figs. 1–4) and dorsal (Figs, 7–8) views. In caudal view, process of tergite 9 with a wide base and a dome-shaped apex (Figs. 6–8). In lateral view, the main epiproct sclerite is long and slender, with a slightly blunted tip, neither upcurved nor downcurved (Figs. 2–3). Dorsal part of apex of epiproct smoothly truncated, in lateral view (Figs. 1–4); ventral part straight. Main epiproct sclerite with a small “hunchback” in its middle section (Figs. 3–4, arrow). Membranous part of the apex of the main epiproct sclerite very long, in lateral view (Figs. 3–4). In dorso-caudal view, the main epiproct sclerite is long and slender, with nearly parallel edges and not swollen medially (Figs. 5, 7–8). Apex of process on tergite 9 at least three times as wide as the tip of the main epiproct sclerite, in dorsal view (Figs. 7–8). Ventral vesicle very large and rounded, its size corresponding to one third of the width of the subgenital plate (Fig. 10). Subgenital plate heart-shaped, as typical for the genus (Fig. 10).

Females (Figs. 11–13). Wing venation as typical for the genus, with the first cell between CuA and CuP in anterior wings quadrangular in shape (Fig. 13; cf. Fig. 55; Aubert 1959: 26, fig. 22; Reding 2020: Vol. 4, fig. 17A20) and not triangular, as in Capnia nigra (Fig. 14) or Capnia vidua. Dorsal edge of femora and tibiae of all three legs with short bristles (Fig. 11). Posterior edge of female subgenital plate crescent-shaped (Fig. 12).

Larvae (Figs. 15–26). Male and female larvae of Zwicknia avilensis sp. n. bear very short and dense erect bristles of nearly equal length on head and pronotum (Figs. 15–17). Setation on basal segments of antennae very short and sparse. Abdominal tergites with very short, but compact bristles (Figs. 18–19). Row of bristles on abdominal tergites medially interrupted (Fig. 18). Lateral bristles on lower margin of abdominal tergites very short, not reaching the adjacent tergite (Fig. 19). Dorsal margin of femur of posterior leg with an uncompacted row of both long and short setae, the longest measuring less than a third of the total width of the femur (Fig. 20). Dorsal edge of tibia of hindleg with a narrow row of long and fine setae in its distal part (Figs. 21–22). Micropterism clearly prefigured on male larvae (Fig. 23). In male larvae and nymphs, tergite 10, which prefigures the male epiproct and the process on tergite 9, with wide basis and blunt apex, in dorsal view (Fig. 24). In lateral view, tergite 10 is smoothly truncated in near mature larvae (Fig. 25) and more pointed in mature larvae (Fig. 26).

The species is named after the region where it was collected, namely the Ávila Province in Spain. The epithet is formed by adding the Latin toponymic suffix –ensis to the place name Ávila and is to be treated as an epicene Latin adjective in the nominative case combined with Zwicknia.

Adult males. From the morphological point of view, Zwicknia avilensis sp. n. stands rather isolated and differs from all other known species or subspecies of the genus Zwicknia from Western and Southern Europe by its headward pointing process of tergite 9 in lateral view (Figs. 1–4), whereas this process is raised perpendicularly in all other known species from these regions (Figs. 27–31), except for Zwicknia rupprechti, where it projects caudally (Fig. 32). In lateral view, the process on tergite 9 is highly elevated in Zwicknia avilensis sp. n. (Figs. 1–4), whereas it is low in Zwicknia rupprechti (Fig. 32) and Z. ledoarei (Fig. 31). In lateral view, the main epiproct sclerite of Zwicknia avilensis sp. n. is slightly pointed (Figs. 1–4), but not acute as in Z. acuta (Fig. 28), Z. westermanni (Fig. 29) and Zwicknia gattolliati (Fig. 30). The epiproct tip of Zwicknia avilensis sp. n. is straight (Figs 1–4), not upcurved as in Zwicknia gattolliati (Fig. 30) or Z. bifrons (Fig. 27). In lateral (Figs. 1–4) and dorsal (Figs. 5, 7–8) views, the main epiproct sclerite of Zwicknia avilensis sp. n. is slender and narrow, whereas it is much thicker and larger in Zwicknia bifrons (Fig. 27; Murányi et al., 2014: 41, fig. 82) and Z. rupprechti (Fig. 32). In lateral view, the membranous part of the apex of the main epiproct sclerite of Zwicknia avilensis sp. n. is very long (Figs. 3–4), much longer than the one of Z. bifrons (Fig. 27), Z. acuta (Fig. 28), Z. rupprechti (Fig. 32; Murányi et al. 2014: figs. 106–109 and figs. 127–147), Zwicknia westermanni (Fig. 29), Z. gattolliati (Fig. 30) and Z. ledoarei (Fig. 31). In caudal view, the shape of the process on tergite 9 has a wide base, is highly elevated and has a dome-shaped apex (Fig. 6), not resembling any of the numerous illustrations of this feature provided by Murányi et al. (2014: 61, figs. 148–164). The ventral vesicle of Zwicknia avilensis sp. n. is very large and rounded (Fig. 10), much larger than the one of Z. ledoarei (Fig. 37; Reding et al. 2016: 141, fig. 5) or Z. rupprechti (Fig. 38; Murányi et al. 2014: 48, fig. 91), but not mussel-shaped as the one of Z. gattolliati (Fig. 36) and Z. acuta (Fig. 34; Murányi et al. 2014: 39, fig. 79), and not elliptical as the one of Z. bifrons (Fig. 33; Murányi et al. 2014: 41, fig. 83) and Z. westermanni (Fig. 35). Note that the ventral vesicle, that males use for generating their bioacoustic drumming signals, is not visible in part of the specimens, because retracted, partly or entirely, under sternite 8 until the start of the drumming activity. The main epiproct sclerite of Zwicknia avilensis sp. n. has a small “hunchback” in its median dorsal region (Figs. 3, 4, arrow), a feature not seen on any other presently described species of Zwicknia (Figs. 27–32) from Western and Southern Europe.

Adult females. In Zwicknia avilensis sp. n., the posterior edge of the female subgenital plate is crescent-shaped (Fig. 12), whereas it is nearly straight in other species, such as Z. bifrons (Fig. 41), Z. ledoarei (Fig. 42), Z. gattolliati (Fig. 43) and Z. westermanni (Fig. 44), except for Z. acuta (Murányi et al. 2014: 34, fig. 64), where it is also crescent-shaped. Like all other known species of Zwicknia, Z. gattolliati excepted (Fig. 40), female adults of Z. avilensis sp. n. have short bristles on the dorsal edge of femora and tibiae of all three legs (Fig. 11; cf. Fig. 39). Zwicknia gattolliati is, to the present knowledge, the only species of the Western Palearctic whose females have long setae on the dorsal edge of their femora and tibiae (Fig. 40; Vinçon & Reding 2018: figs. 8 and 11; Reding 2021).

Larvae. In larvae of Zwicknia avilensis sp. n., the erect bristles on head and pronotum are dense, compact and very short (Figs. 15–17), even the shortest among all other larvae of Zwicknia examined so far (Z. bifrons, Z. westermanni, Z. ledoarei, Z. rupprechti and Z. gattolliati; Reding 2020: Vol. 4, figs. 17A2, 17A14, 17B9, 17C3 and 17C4). The bristles on the head of Zwicknia rupprechti are also very short, but uncompacted (Fig. 52; cf. Figs. 15, 17). In lateral view, tergite 10 of mature male larvae of Zwicknia avilensis sp. n. is smoothly truncated (Fig. 25), or slightly pointed (Fig. 26), and different from those of Capnia vidua (Fig. 45), Capnia nigra (Fig. 46), Zwicknia westermanni (Fig. 47), Z. bifrons (Fig. 48), Z. ledoarei (Fig. 49), Z. gattolliati (Fig. 50) and Z. rupprechti (Fig. 51).

The type material of Zwicknia avilensis sp. n. has been collected above 1000 m in the Sierra de la Serrota, located within the mountain ranges of the Sistema Central, in small temporary brooks in the headwaters of the Duero basin (Fig. 56). The collection dates for the species indicate a winter flight period, from December to March. Isolated females, however, are still found in April, when no males are on the wing anymore. The overall distribution of Zwicknia avilensis sp. n. in Spain is presently unknown. The species inhabits brooks and rivers that dry up in summer (Fig. 56; González del Tánago 1984). In December 2020, the species was found with Leuctra maroccana Aubert, 1956c and Capnioneura libera; in April 2021 with Brachyptera arcuata (Klapálek, 1902) and Protonemura asturica (Aubert, 1954).

In 1981, the species was reported from 14 different sampling stations in the headwaters of river Duero (González del Tánago 1984). In 2020 and 2021, the species is still extant in at least one of its former locations (samplings by the second author). Further collecting is needed to ascertain the present conservation status of the species.

Identification key for adult Zwicknia from Western and Southern Europe