Type material. Holotype (MNCN15.05/60147H): Spain, Prov. Gipuzkoa, Oñate,Valle de Araotz, Cueva de la Ermita de Sandaili, UTM 30TWN4580260906, N42.999442, E-2.438076, alt. c. 400 m, moist, muddy walls in karst cave, 15.11.1984, leg. C. Prieto, B. Gómez & K. Altonaga.

Paratypes: locus typicus: 53 shells (UPV/EHU-FC: 74) and 4 dried snails (UPV/EHU-FC: 75), data as the holotype; 41 shells (UPV/EHU-FC: 549), 18.06.2011, leg. C. Prieto, A. Jochum, A. Weigand, R. Slapnik & J. Valentinčič; 6 shells (MNCN15.05/60147P, ex UPV/EHU-FC: 549), ibid.; 6 shells (SMF 341634, ibid.), ibid.; 6 shells (RMNH.5003914, ibid.), ibid.; 6 shells (NMBE 529864/6, ibid), ibid.; 19 shells (AJC/1864), ibid.

Other material. (Fig. 2): Prov. Bizkaia: Yurre, Urkizu, Cueva de Otxas, UTM 30TWN2050081208, N43.183362, E-2.747741, alt. c. 500 m, 18.01.1981, leg. B. Gómez, R. Martín, K. Altonaga, 23 shells (UPV/EHU-FC:24); same locality, 19.06.2011, leg. C. Prieto, A. Jochum, A. Weigand, R. Slapnik & J. Valentinčič, 30 shells (MCBI CSR SASA 40115), ibid., 20 shells (AJC/1867), ibid. 11 shells (RMNH.5003916); Mañaria, Cueva de Silibranka-2, UTM 30TWN2741175235, N 43.129357 E -2.662995, alt. 220m, 20.06.2011, leg. C. Prieto, A. Jochum, A. Weigand, R. Slapnik & J. Valentinčič, 80 shells (UPV/EHU-FC:557), ibid., 5 shells (MCBI CSR SASA 40090), ibid., 18 shells (AJC/1851), ibid. 10 shells (RMNH.5003915); Dima, Indusi, Cueva del Cráneo, UTM 30TWN2157275145, N43.128736, E-2.734786, alt. c. 400 m, 20.06.2011, leg. C. Prieto, A. Jochum, A. Weigand, R. Slapnik & J. Valentinčič, 13 shells (UPV/EHU-FC:556), ibid., 13 shells (AJC/1853).

Shell ca. 1.2 mm, transparent, elongate or elongate-conical with an entire, roundish and more or less thickened peristome, lacking obvious apertural barriers, but often with an obsolete lamella (denticle) in the parieto-columellar corner; columella with a single, low annular lamella.

(material from type locality). Measurements of holotype and paratypes are provided in Table 1.

Shell minute, rather variable in height (on average ca. 1.2 mm), conical to elongate-conical with about 5 whorls, regularly coiled, suture deep, whorls convex, more or less strongly shouldered, especially in the more conical shells; teleoconch sculpture of fine, occasionally almost rib-like, axial striae; weak axial ribbing immediately behind the palatal-basal lip, occurring for a short distance; aperture more or less circular; peristome closely adhering to spire, reflected, moderately thickened, roundish, but often somewhat higher than wide or wider than high, taking up ca. 40% of shell height; umbilicus closed, umbilical depression deep, with fine or coarser, sometimes almost rib-like, axial striae; apertural barriers absent apart from a rather low lamella (appearing as a tiny denticle) on the parietal-columellar corner, discernable only in oblique apertural view; columella with a single, low annular lamella, only visible in body whorl at some distance from aperture.

Differs from Zospeum biscaiense by the smaller, more elongate shell and the absence of major apertural barriers; from Zospeum schaufussi (sensu Gittenberger 1980) by the roundish peristome; Zospeum suarezi is generally smaller, and has a more elaborate, two-tiered arrangement of lamellae on the columella; in Zospeum bellesi, apertural barriers and columellar ornamentation are completely absent.

The new species is named after the pre-Roman Era Vascones Tribe (from Latin gens Vasconum), which at the arrival of the Romans during the 1^st century, inhabited a territory spanning the region between the upper course of the Ebro River and the southern basin of the western Pyrenees. This tribe is considered (disputed) the ancestor of the Basque People.

Sierra de Aitzgorri and the adjacent Sierra de Aramotz-Anboto in the Provinces of Gipuzkoa and Bizkaia, Spain (Fig. 2). Both massifs are formed in Lower Cretaceous (Urgonian) limestone bedrock and separated by the valley excavated by the Deba River.

Live Zospeum vasconicum were found in Cueva Arrikrutz on densely perforated mats of fine mud lining the walls of the upper level of the cave. In the immediate vicinity of this colony, numerous translucent Zospeum shells were found embedded in a thick, uniform layer of mud, superficially interspersed with yellow, clumped strands of fungal aggregations (Fig. 8A–B). Only single live individuals of Zospeum vasconicum were found on the walls of Cueva de la Ermita de Sandaili. No bats or bat guano were seen in the vicinity of the collection site.

In the caves where this species occurs (see above), fresh empty shells were found in relative abundance at various spots within these caves, suggesting that the species commonly occurs there, and that these populations are not immediately threatened. Still, on a global scale, its distribution is likely limited to less than 5 caves within a radius of less than 20 km². In conjunction with the categories for the IUCN Red List (IUCN Standards and Petitions Subcommittee 2014), it is considered a vulnerable, narrow range endemic (Vu, D2). Habitat disturbance by unrestricted tourism may pose the largest threat. The cave entrance of Cueva de la Ermita de Sandaili contains a chapel, is openly accessible and is not protected as an entity within a natural park. Neighbouring Cueva Arrikrutz belongs to the Natural Park of Aizkorri-Araotz and opened for tourism in June 2007.

Although the populations studied in this paper were collected from currently non-contiguous caves, which are geologically part of two adjacent limestone complexes i.e. Otxas, Cráneo and Silibranka-2 of the Aramotz-Anboto massif and Sandaili of the Aizkorri massif, these populations were found to be very closely related, sharing identical or very similar CO1, 16S and H3 sequences (Weigand et al. 2013). However, morphologically, significant differences exist between these populations. Although shell dimensions are quite variable, even within populations, populations differ more or less in shell size and shape (see Table 1). Shells from the type locality and from Cueva del Cráneo, are on average, smaller, significantly less slender, have less whorls and a proportionately larger body whorl than those from Cueva Silibranka-2 and Cueva de Otxas, but the range of some characters overlap. These populations are not different in spire angle and coiling tightness. Shells from Cueva del Cráneo seem to have larger peristomes than specimens from the other caves. Observed are additional qualitative differences between the populations such as in sculptural texture (coarseness of rib-striation; ribbing behind palatal lip present in type locality and Cueva del Cráneo, indistinct or absent in Silibranka-2 and Otxas); whorl profile (topotypic shells have more convex and more strongly shouldered whorls than e.g. the Silibranka-2 population), as well as in the expression of the parieto-columellar denticle (obsolete or absent in Silibranka-2 but generally present in shells from the other caves). In some Cueva de Otxas shells, the peristome is slightly detached from the spire (Fig. 5C). We restrict the type material to (selected) shells from the Cueva de la Ermita de Sandaili. However, material documented by Jochum et al. (2012) from the neighbouring Cueva Arrikrutz within the Natural Park of Aizkorri-Araotz, Oñate (N42.997222, W2.428076), is likely also to be Zospeum vasconicum. The nearest passage of the Arrikrutz-Gesaltza cave system is less than 150 m from the Cueva de la Ermita de Sandaili on the other side of the river. However, the Arrikrutz material was not molecularly assessed by Weigand et al. (2013).