Zospeum percostulatum, Alonso, Alvaro, Prieto, Carlos E., Quinonero-Salgado, Sergio & Rolan, Emilio, 2018
Alonso, Alvaro, Prieto, Carlos E., Quinonero-Salgado, Sergio & Rolan, Emilio, 2018, A morphological gap for Iberian Zospeum filled: Zospeumpercostulatum sp. n. (Gastropoda, Eupulmonata, Carychiidae) a new species from Asturias (Spain), Subterranean Biology 25, pp. 35-48: 36-41
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Zospeum percostulatum sp. n.
Cueva de La Herrería (also known as Las Herrerías or La Mina) (43°23.98'N, 4°45.95'W, 30TUP5700006726, 45 m), La Pereda village, municipality of Llanes (Asturias) (Fig. 1). The cave has a wide entrance, 2.5 m high, forming a deep shelter, continued by a short gallery on the left, about 20 m long, that leads to a series of small chambers, with height decreasing towards the end to less than 1 m. Most of the right side of the cave is labyrinthic and, because of its low height and the density of columns, some parts are almost impenetrable. Descending south-west from the smaller secondary entrance, there is a large (but quite low) diamond shaped chamber with four openings. To the south, this chamber leads to a long gallery with signs of sporadic hydraulic activity. To the west, protected by a fence, there is a chamber where one of the few samples of not figurative prehistoric painting in the north of Spain can be found, consisting of red grills made by parallel lines enclosed in a quadrangular contour, but lacking any signs of animal figuration ( Jordà and Mallo 1972).
This cave was firstly named as Cueva de Bolao by Jeannel and Racovitza (1915) in their account of the exploration made in 1913 by the archaeologist H. Breuil. Cueva El Bolao was treated in some works as a nearby -but different- cave. Our explorations on the surroundings of La Herrería seem to confirm the suspicion of Bolívar (1923), who first pointed that El Bolao and La Herrería may be just two different names of a single cavity.
Holotype, a complete specimen (in etanol 96°) [ MNCN 15.05/200017H, ex ZUPV-4885], 18.07.2017, Á. Alonso, C. Prieto, S. Quiñonero-Salgado, J. Ruiz-Cobo leg.
Paratypes: 16 adult shells and 5 complete specimens [ZUPV-4885]; 50 adult shells [ZUPV-4913]; 30 adult shells [CAA-0737-A]; 25 adult shells [CSQS]. Paratypes from the sample ZUPV-4914 will be housed also in MNCN [15.05/200017P], Naturhistorisches Museum Wien and Naturalis Biodiversity Center.
40 adult shells [ZUPV-4863]: Cueva Collubina (43°23.94'N, 4°43.37'W, 30TUP6048806568, 45 m), San Roque del Acebal, municipality of Llanes (Asturias), 18.07.2017, Á. Alonso, C. Prieto, S. Quiñonero-Salgado, J. Ruiz-Cobo leg.
Species characterized by a relatively large shell, if compared to other Spanish Zospeum species, raised spire, ribbed surface, ovate opening, continuous peristome and absence of apertural teeth or internal lamellae.
(Figs 2-4). Shell 1.4-1.8 mm in length, fragile, hyaline when fresh, elongate to conic-ovate in smaller shells, with spire formed by 5-5.75 whorls. Protoconch (Figs 2F, 3 B–D) rounded, somewhat globose, apparently smooth, with a small core and a very wide first half whorl, with a smooth surface that extends for a little more than a whorl, reaching a diameter of 0.4 mm. At high magnification it can be seen that the shell surface is full of spirally aligned small depressions formed by dots or short lines (Fig. 3 C–D).
Teleoconch has about four well convex whorls, slightly shouldered and separated by a deep suture. These whorls present a sculpture of prosocline, narrow, sharp ribs with a rounded profile, somewhat irregularly arranged and sometimes incomplete, without reaching the inferior suture; its number and robustness increases every whorl and in the last one it can be 50 or more (8-10/0.5 mm).
Last whorl is near 60 % of the shell height, a bit more in smaller shells, barely and progressively ascending towards the aperture, where the rear ribs are somewhat closer together. Aperture ovoid, somewhat oblique, with almost vertical columellar border, rounded outer edge and parietal edge delineated by a parietal callus, thickened in more stylized shells. Peristome reflected, sometimes bilabiate, and thickened, especially in the columellar border. Last whorl without internal formations, with cylindrical colu mella, 0.15 mm in diameter. Umbilicus shallow, with imperceptible umbilical groove. Shell surface seems smooth, but irregular longitudinal lines crossed with little marked spiral lines can be seen at high magnification (Fig. 3 F–G).
The holotype shell measures 1.59 mm height and 1.00 mm width (Fig. 2 A–C), and the body whorl reaches 58 % of the shell height. Morphometric data from the type locality and Cueva Collubina (Table 1, Fig. 5) indicate that both populations are somewhat distinct, being formed the later by somewhat smaller individuals with more closer riblets per whorl.
The specific epithet refers to the ribbed surface of the shell in diminutive ( ‘costulata’) with the Latin prefix ‘per-’ (meaning ‘very’) to emphasize the best diagnostic character with regard to the remaining Iberian species.
Strict troglobiont living on wet, concretionated cave walls covered by a clay film, although it can also be found on the ground, under concretion fragments. Some shells were collected at only 35 m away from the cave entrance. Empty shells are much more abundant than live individuals, which are much harder to find because their transparent shell and light cream color camouflages them with clay and concretions. Due the absence of decalcification in empty shells, these can last a long time (perhaps centuries) and accumulate by hundreds in a litter of clay sediments at the foot of cave walls. This species shares its biotope with a distinctly smaller Zospeum species belonging to a conchological suarezi species group (see Discussion) although a topographical differentiation cannot be discarded. More external sites for Zospeum in Cueva de la Herrería (Fig. 1) mostly provided Z. percostulatum sp. n., with only a few empty shells of Z. cf. suarezi , whereas the most internal site provided all found living snails of this last species, many individuals in close vicinity on corrugated patches of clay, as depicted by Jochum et al. (2012: Fig. 2), but only a few empty shells of the larger Z. percostulatum in a proportion of 10:1. A similar microtopographical distribution has been observed in other caves from the Basque region (C. Prieto, unpub. obs.) where the smaller species concentrates on clay patches and the larger species wander lonely on stalactites and concretionated walls.
Regarding the biocoenosis of the cave, no other strict troglobiont gastropods (i.e. Cryptazeca ) were found, and only some common species like Oxychilus sp. or Elona quimperiana (Blainville, 1821) seem to live inside. Other troglobiont species are the coleopterans Laemostenus peleus (Schaufuss, 1861), Breuilia triangulum (Sharp, 1872) and Quaestus occidentalis (Jeannel, 1911) ( Jeannel and Racovitza 1915; Español 1954; Collado 1977). Jeannel and Racovitza (1915) recorded the finding of springtails, diplopods and isopods but apparently they were never published.
Zospeum percostulatum sp. n. has been found in two caves 3.5 km far away from each other, placed in the lower part of northern foothills of Sierra de Cuera (Fig. 6). This sierra, a calcareous east-west formation of about 25 km in length and up to 1315 m high, not yet investigated for the genus Zospeum , is separated from the Picos de Europa by the Cares river, on whose northern foothills are placed the caves cited for Z. suarezi and Z. schaufussi . The distance between these caves and those inhabited by Z. percostulatum sp. n. is about 12-15 km.
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