Type material. Holotype (MNCN15.05/60148H)): Spain, Prov. Burgos, Berberana, Monte de Santiago, Cueva de Las Paúles, UTM 30TWN0062054680, N43.1282, E-2.73618, alt. c. 840 m, moist, muddy walls in karst cave, 09.11.2013, leg. C. Prieto.

Paratypes: locus typicus: 8 specimens (MNCN15.05/60148P ex UPV/EHU-FC:1608) and 2 shells (NMBE 529904/2), 2 shells (SMF 341635) and 2 shells (RMNH.5003943), data as the holotype. 1 shell (UPV/EHU-FC:64), 12.02.1984, leg. P. Zaldívar. 2 shells (MNCN 15.05/60149, ex UPV/EHU-FC:70) and 3 shells (UPV/EHU-FC:72), 11.11.1984, leg. C. Prieto, B. Gómez & P. Zaldívar, 9 specimens (UPV/EHU-FC:559), 21.06.2011, leg. C. Prieto, A. Jochum, A. Weigand, R. Slapnik & J. Valentinčič. 7 specimens + 5 shells (UPV/EHU-FC:560), ibid., 3 specimens molecularly processed (Weigand et al. 2013), 7 shells (4 broken) (AJC/1877), ibid., 5 shells (broken) (MCBI CSR SASA 40598), 11.11.1984, leg. C. Prieto & B. Gómez, 3 shells (RMNH.234152).

Shell turbinate-conical with approximately 5 ½ regularly coiled, convex, rounded whorls, transparent, comparatively large; columellar and palatal-basal lip narrowly reflected; umbilicus closed, umbilical depression deep.

Measurements are provided in Table 2.

Shell minute, turbinate-conical, with approximately 5 ½ regularly coiled, convex, rounded whorls; shell transparent when fresh, chalky white with age, comparatively large, rather variable in shape; teleoconch sculpture of irregular axial striae or blunt growth lines, often crossed by an equally superficial spiral element, some distinct axial ribbing may be present for a short distance immediately behind palatal-basal lip; last whorl large and tumid, encompassing ca. 2/3 of shell height; aperture lunate; peristome somewhat higher than wide, closely adhering to spire, taking up about half of the shell height, angular, with a thin, straight parietal callus; apertural dentition usually consisting of a small, short lamella on the parietal wall and a tooth on the parietal-columellar corner of the peristome (barely conspicuous in frontal view (Fig. 6A), best discernable in a slightly oblique, apertural view (Fig. 6D)); apertural barriers can however, be entirely absent (Fig. 7D); columella with a single, low, lamella-like dilatation (Fig. 7G), only visible in body whorl at some distance from the aperture.

Though comparatively large amongst Iberian species, the Zospeum zaldivarae shell is minute (shell height ca. 1.5 mm) and turbinate-conical in form. It is however, larger, wider (ca. 1.2 mm) and less elongate than other known Iberian Zospeum species except Zospeum biscaiense. Zospeum biscaiense has a more tightly coiled shell with palatal-basal apertural barriers.

The new species is named after Mª Pilar Zaldívar, a biologist and speleologist from the Niphargus Speleological Team, who discovered the species in the 1980’s.

Only known from the type locality.

Zospeum zaldivarae was found sparingly in a muddy sediment matrix of somewhat coarse, vermiform texture interspersed by clumped aggregations of yellow- and white-coloured fungi (Fig. 8C) (Jochum et al. 2012 fig. A–B). No bats or bat guano were seen in the vicinity of the collection site. The species was found syntopically with Zospeum suarezi.

Zospeum zaldivarae is only known from the Cueva de Las Paúles. Consequently, and in conjunction with the Guidelines for the IUCN Red List (IUCN Standards and Petitions Subcommittee 2014) it is a vulnerable, narrow range endemic (Vu D2) and as such, warrants immediate conservation priority. Although this cave belongs to the Natural Monument of Monte Santiago, it is nonetheless relatively easily accessible to the public.

Zospeum zaldivarae appears to be polymorphic in the presence/absence of apertural barriers. These barriers were not noticed in the material sequenced by Weigand et al. (2013), but their presence cannot be excluded. However, we have little doubt that the dentate and edentate specimens co-occurring at the type locality are conspecific.

Zospeum zaldivarae is conchologically quite different from most other Iberian Zospeum species hitherto described. In shape, it best resembles Zospeum biscaiense. These two species share a wide shell with a reniform aperture and an angular, not roundish, peristome with a straight palatal-columellar callus. Also, phylogenetically, this species is distinct (Weigand et al. 2013) and possibly more closely related to Zospeum biscaiense.