Zospeum percostulatum sp. n. from Cueva de La Herrería (Llanes, Asturias) is described. It is characterized by a relatively large shell (1.4–1.8 mm height), conical, with ovate aperture, continuous peristome and thickened parietal callus; shell costulate except two first whorls; without any sort of inner formations. It is the first clearly costulate Iberian species, filling a morphological gap in the Iberian clade, and the largest species from the Cantabrian region, being the first species described from Asturias.

Se describe Zospeum percostulatum sp. n. de la Cueva de La Herrería (Llanes, Asturias), caracterizada por una concha relativamente grande (1.4–1.8 mm de longitud), cónica, con abertura ovalada, peristoma continuo y callo parietal engrosado; superficie costulada excepto en las dos primeras vueltas y carente de cualquier rastro de formaciones internas. Es la primera especie ibérica nítidamente costulada, lo que llena un hueco morfológico del clado ibérico, y la de mayor tamaño de la región cantábrica, y es la primera especie descrita de Asturias.

Cave-dwelling species, troglobiont gastropod, microgastropod, shell variability, ecology

Especie cavernícola, gasterópodo troglobio, microgasterópodo, variabilidad conquiológica, ecología

The genus Zospeum Bourguignat, 1856 is the only troglobiont genus of land snails present in the Iberian Peninsula, and has also been for a long time the only troglobiont genus of the family Carychiidae until the recent description of the genus Koreozospeum (Jochum et al. 2015a). The geographical distribution comprises two disjunct areas: eastern Alps and Dinaric Alps from where about twenty species are known (Bole 1974; Pezzoli 1992; Slapnik and Ozimec 2004; Weigand 2013; Jochum et al. 2015b), and the Pyrenean-Cantabrian region from where six species have been described so far. The first Iberian species described was Zospeum schaufussi Frauenfeld, 1862, collected inside an unknown Spanish cave by L. Schaufuss and briefly described with 16 words (Frauenfeld 1862). Unaware of the occurrence of any Zospeum species in western Europe, Gittenberger (1973) attributed the novelty to Zospeum bellesi Gittenberger, 1973, from the Cueva de Aso (northern part of Huesca province). Realizing that Zospeum is more widely distributed than in the Pyrenees, Gittenberger (1980) revised new Iberian material and the type material of Z. schaufussi, revalidating the already known species and further describing Zospeum suarezi Gittenberger, 1980 from a cave in Puente Viesgo (Cantabria) and other Cantabrian caves. Gómez and Prieto (1985) described Zospeum biscaiense, an odd toothed species from Cueva de Otxas in Yurre (Bizkaia), and more recently Jochum et al. (2015c) have described Zospeum vasconicum Prieto, De Winter, Weigand, Gómez & Jochum, 2015 from several caves from Bizkaia and Gipuzkoa provinces, and Zospeum zaldivarae Prieto, De Winter, Weigand, Gómez & Jochum, 2015 from Cueva de Las Paúles in Berberana (Burgos). Meanwhile, Weigand et al. (2013) had already demonstrated the molecular divergence between those two species and four genetic lineages conchologically grouped under Zospeum suarezi, thus evidencing that the biodiversity in the Cantabrian region is still far from completion.

Although based on an incomplete species sampling, both Alpine-Dinaric and Cantabrian species groups of Zospeum have been recovered as monophyletic sister clades (Weigand et al. 2013), but no morphological synapomorphies have been found for any of them. With respect to the Pyrenean-Cantabrian clade, a wider morphospace in the Alpine-Dinaric clade is evident, as exposed by Kobelt (1898, pl. 218–219) or Bole (1974), with small to large (up to 2.5 mm height), globose to slender, round to widely auriculate aperture, edentate to heavily toothed, smooth to ribbed species. On the contrary, Iberian diversity is restricted to smaller (less than 2mm), smooth, edentate species, with the only exception of the dentate Z. biscaiense.

The finding of a population with sharply costulated and relatively large shells allow us to describe it as a new species, since all known Iberian species have smooth shells, and only in one of the Cantabrian species, Z. zaldivarae, shells reach 1.6 mm in height (Jochum et al. 2015c).

The material studied has been gathered up mainly by flotation of fully desiccated clay sediments collected at the foot or holes of the walls where white, empty shells, have been detected. Shredded sediment was sieved through a fine mesh, then submerged in water, so most part of intact shells, together with organic remains, passes to the flotsam due to the formation of a bubble air inside them. Live individuals have also been collected through direct search on concretionated cave walls covered by a wet film of percolated clay.

SEM photographs were obtained with a Quanta 200 microscope; the other photographs are combined images produced through the Heliconfocus v.6.7.1 software from series of photographs obtained with a Nikon DS5M camera mounted on a stereomicroscope Nikon SMZ-1500. Shell measurements were done using the image analysis software of the Nikon DS5M camera. The analysis of the measurements was done with the PAST software (Hammer 2017) and the distribution map with the DMAPW software (Morton 2004).

Shell morphology alone cannot be seen as sufficiently informative for recognizing microgastropod species of Zospeum, at least in certain species-groups, as was evidenced by Weigand et al. (2013) by identifying four genetic lineages having shells like Z. suarezi (but see e.g., Jochum et al. 2015b). Although more integrative evidence as anatomical or molecular data is desirable, the description of new clearly recognizable taxa cannot be hindered by arguing the absence of genetic data, which is the rule for most of marine or other subterranean micromolluscs, inclusively with the erection of supraspecific taxa (e.g., Jochum et al. 2015a). As Zospeum percostulatum sp. n. is the only one Iberian species with ribbed shell, the possibility that future genetic analyzes do not confirm their uniqueness is unlikely.

The two westernmost Iberian species, Z. schaufussi and Z. suarezi, have been recorded for Asturias in two nearby caves from Cabrales, both from Cueva de Inguanzo and the later also from Cueva de los Quesos (Gittenberger 1980). Strikingly, Gittenberger (1980) drew the unique published sketch for each species from shells from Cueva de Inguanzo, being in fact the conchological reference for both species. However, considering that the type locality of Z. suarezi is 70 km far eastward, that there are four (at least) cryptic species with similar conchological features (Weigand et al. 2013) and that the description of Frauenfeld (1862) for Z. schaufussi does not match with Gittenberger’s drawing and description, the true identity of Asturian records is doubtful. Therefore, Zospeum percostulatum sp. n. can be considered the first unequivocal Asturian species.

Zospeum percostulatum sp. n. has been found syntopically with another Zospeum species having a smaller size, conical shell with well convex whorls, smooth surface, round aperture with continuous peristome and inner columellar lamella which pokes at the opening. These conchological features allow ascribing this second species to a species group, which would be integrated, at least, by the four genetic lineages evidenced by Weigand et al. (2013) and cited as Zospeum suarezi. They recognized that the populations of Bosque (Inguanzo), Linar (La Busta), Las Paúles and Los Cuervos (Bizkaia) caves represent different species with a similar conchological morphology. This suarezi species group includes also another genetic lineage for populations from eastern Bizkaia and western Gipuzkoa caves, which were conchologically recognized as a new undescribed species by Altonaga et al. (1994) many years before its description as Zospeum vasconicum (Jochum et al. 2015c). For the moment, due to the complexity of this open question, which increases with nomenclatorial aspects related to Z. schaufussi, we do not address the issue of the identity of this companion species.

No graphical representation of the conchological morphospace occupied by Zospeum species has been yet published. As exposed before, Alpine-Dinaric taxa would constitute a monophyletic clade (Weigand et al. 2013) much more diverse than the Pyrenean-Cantabrian sister clade. Apart from tripling the number of known species, some of them have no conchological counterpart in the Iberian Peninsula, as Z. spelaeum costatum (Freyer, 1855), a large, strong ribbed species showing a carychioid facies, with well developed lamellae reaching the apertural plane, and also palatal teeth. On the contrary, Z. biscaiense with two apertural parietal lamellae, two palatal teeth and without inner lamellae (Gómez and Prieto 1985) has no counterpart in Alpine-Dinaric taxa.

Some Zospeum species of the Alpine-Dinaric region present a wide variability as shown by Bole (1974) or Pezzoli (1992), both in sculpture and development of aperture formations as well as in size and diameter, being obviously greater in species with wider geographic range. Thus, Pezzoli (1992) gives a size range for Z. globosum of 1.2–2.2 mm, even with some cavities in which two clearly distinguishable morphologies are present (eg. Grotta del Soglio: standard shape, 1.6–1.7 mm and turreted shell, 2–2.1 mm). Such wide variability has not been described for any Iberian species although Gittenberger (1980) cites a size of 1.3–1.9 mm for Z. bellesi.

The presence of conspicuous and prominent axial ribs constitutes a taxonomic character that until now has not been indicated for Iberian species, so Z. percostulatum sp. n. can be differentiated immediately from all of them. Furthermore, this new species fills one of the conchological gaps – the lack of ribbed species – between Alpine-Dinaric and Pyrenean-Cantabrian taxa. Occasionally, some shells of the known Iberian species have some stronger streaks, especially under the suture, taking the aspect of incomplete riblets but in Z. percostulatum sp. n. ribs form a constant and regular pattern. In addition, the new species has relatively large shells, reaching 1.8 mm length, in comparison to the other Cantabrian species, whose largest shells barely reach 1.45 mm height (Gittenberger 1980), making its recognition and discrimination easier.

In Cueva Collubina, 3.5 km eastward from the type locality, we have found shells attributable to Z. percostulatum sp. n., but they are somewhat smaller and wider, with more auriculate aperture, thinner parietal callus and finer and tighter ribs. Although they could be minor differences linked to geographical isolation, we consider that these individuals belong to the same species.

The SEM photographs were made by Inés Pazos in the Centro de Apoyo Científico y Tecnológico a la Investigación (CACTI) of the University of Vigo. We also thank Jesus Ruiz-Cobo for his cooperation in field samplings, Joaquín López Soriano for comments and correction of grammar and language, and referees (A.Weigand, E.Gittenberger & E.Neubert) for the improvement of the manuscript. Participation of C. Prieto was funded by the Basque Government through the Research group on “Systematics, Biogeography and Population Dynamics” (IT575-13).