The terrestrial gastropods (Mollusca: Gastropoda) of the Mavrovo National Park, North Macedonia

: Sixty-one species taxa of land gastropods are known for Mavrovo National Park, and 34% of them are species taxa of high conservation value. Considering the unsystematic surveys in the area, it can be assumed that in the future the number of species taxa will significantly increase. The status of Mavrovo as a national park under high protection, and there are no immediate threats to the malacofauna. Potential problems for invertebrate communities, including snails, would be big destructive changes in their habitats and especially the presence of hydropower projects and stone quarries. The protection of the species habitats from human activity and different types of modification is the best protection measures for the mollusk fauna in Mavrovo National Park.


Introduction
Mavrovo National Park (Mavrovo NP) is the largest protected area in North Macedonia.Mavrovo NP is located in the northwestern part of the country and covers the area around lake Mavrovo, the upper and lower streams of the Radika River, as well as the Mountains of Korab, Deshat, the southwestern ends of the Shar Mountain, the greater part of Bistra and the northern parts of Krčin.The park protects high diversity of habitats and numerous rare and endemic animals, plants and fungi, and a significant part of its territory has a carbonate base (SSO, 2011;Melovski et al., 2013).While plant and vertebrate diversity is relatively well studied, knowledge of invertebrates, especially for land snails, is rather poor and fragmentary.

Materials and methods
The gastropods were collected by classical hand collection, soil-traps and by non-quantitative use (without exact volume of collected soil) soil sampling method (Dedov & Antonova, 2015).The method consists of collecting soil from suitable habitats.Each sample, in addition to the soil layer, also contains leaves and living plants from the corresponding square ("biomass sample").The resulting sample is immersed in a standard bucket filled with water.The fraction that floats to the surface of the water is taken with a suitable plastic strainer.Using a rectangular plastic plate, the sample is transferred in a mesh (a thin stocking), and left to dry.The sample is then sieved under laboratory conditions through a system of sieves with different hole sizes.The fractions are examined under binoculars to separate the shells from the remaining particles in the sample.When each sample is collected, the point is marked with GPS.The sampling localities are present on Supplementary material 01 � and illustrated in Fig. 1.The full names of the species reliably recorded in the park and its immediate surroundings are given in Supplementary material 02 �.

Results
In total, 67 species of land snails and slugs were reported in the previous "Management Plan of Mavrovo National Park for the period 2012-2021, Annex -Mollusca: Gastropoda and Bivalvia" (Petkovski, 2011).Forty-four species from that list were confirmed during our field surveys (Supplementary material 02 �).Five species were not collected in the cur-rent study but are reliably reported in the literature: Chondrula tridens, Gyralina korabensis, Laciniaria plicata, Vallonia costata and Xerolenta obvia (Pavlović, 1911;Riedel, 1985).
Twelve species from the previous plan (Petkovski, 2011) have not been confirmed in the field, nor have reliable records of their presence in the park been found in the literature reviewed, but are very likely to occur within the boundaries of the protected area: Arion circumscriptus Johnston, On the other hand, 15 species new to the Mavrovo NP were found during the field research (cf.Petkovski, 2011): Acanthynula aculeata, Arion silvaticus, Carychium minimum, Galba truncatula (an amphibious species often included in the lists of both freshwater and terrestrial snails), Gittenbergia sororcula, Lehmannia brunneri, Montenegrina perstriata mavrovoensis, Montenegrina perstriata perstriata, Perpolita hammonis, Punctum pygmaeum, Pupilla alpicola, Tandonia albanica, Truncatellina claustralis, Vertigo antivertigo and Vitrea botterii.Some of these species have been reported for localities in the park from publications not reflected in the previous plan.
The species Perpolita hammonis is recorded for the first time for the North Macedonian fauna (Fig. 2).For Helicigona korabensis there is no scientific confirmation of its occurrence in North Macedonia.In the current survey we confirm the species for the North Macedonian part of Korab Mountain (for details see Subai, 1997) (Fig. 3).Deroceras laeve is reported for Mavrovo NP by Wiktor (1996).Thus, a total of 61 species taxa of land snails are reliably known for Mavrovo NP (Supplementary material 02 �).

Taxonomy
According to Bank & Neubert (2017) the subspecies Cochlodina laminata albanica Jaeckel, 1956 is present in North Macedonia.The type locality of this taxon is Daiti Mountain, near Tirana, the capital of Albania but it also occurs in the area from Bosnia to Albania and (North) Macedonia.Compared to the nominate subspecies Cochlodina laminata albanica it is characterised by its lighter shell with yellowish to yellowish-brown coloration and distinct shell striation (Gittenberger, 1967).Similar shells were found in Mavrovo NP.According to Gittenberger (1967), another subspecies of C. laminata -Cochlodina laminata oreinos (A.J. Wagner, 1914) could be found in the northern parts of the Shar Mountain (Ljuboten).This subspecies is most likely the high-mountain form of Cochlodina laminata albanica, and could be distinguished from it by its the compactly fusiform and irregularly striated shell, as well as weakly reduction clausiliary apparatus.Because of the unclear status of the Cochlodina laminata subspecies and the lack of a clear isolation barrier between different populations in the region, we refer all specimens to the nominate species.
According to Petkovski (2011) Morlina glabra (Rossmässler, 1835) and Morlina glabra striarius (Wrsterlund, 1881) are found in Mavrovo NP, but only the subspecies M. glabra nitidissima is present in the western part of North Macedonia.This is confirmed by our findings.
Perpolita hammonis (Fig. 2) was found in pitfalltraps set in the high-mountain wetland "Lukovo Pole" of Shar Mountain.The taxon represents a new genus and species for the fauna of North Macedonia.This species is typical for acid soils, moderately humid or swampy habitats (Welter-Schultes, 2012) Helicigona korabensis (Fig. 3B) was described by Subai (1997) from the Albanian part of Korab Mountain.We recorded this species from two sites in North Macedonia: high-mountain parts of Korab (Mala Planina Ridge, under Visoko Brdo Peak and Kepi Bard 2 Peak, near Boazi Peak).According to Mollus-caBase (2023) the status of this species is uncertain and it is 'taxon inquirendum'.We were not able to find any live adult specimens, so we are not sure of the exact genus of the species.We found shells and a juvenile only in high-mountain areas, in low abun-dance, on both silicate rocks with limestone admixture and pure limestone rocks.In our opinion, it is a valid species, endemic to the high areas of Korab Mountain.

Species with high conservation value
Twenty-one land snails of high conservation value were found in the in Mavrovo NP.This number includes: Macedonian endemic (6 species) and 13 Balkan endemics (Welter-Schultes, 2012).According to the IUCN European Red List of Threatened Species (Neubert et al., 2019), Euxinella radikae and Gyralina korabensis are considered as Near Threatened (NT) (Supplementary material 02 �).
Two species have been identified as a food resource: Helix lucorum and the Balkan endemic Helix vladica.Although it is not yet known whether the second species is collected for food, it is difficult for nonspecialists to distinguish it from Helix pomatia which is popular among the snail-collectors.Thus, we assume that Helix vladica is also collected for food by the local population.

Localities and habitat important for the biodiversity of land gastropods
As mentioned above, the area of Mavrovo NP is not well studied from the point of view of land snails' diversity, but based on the available information, the high mountain area of Korab, especially the carbonate rocks and grasslands on the path from Karaula Strazimir to Golem Korab Peak can be defined as particularly important for the biodiversity of land gastropods.Many endemic species inhabit the carbonates, including in and around the caves along the Radika River, as well as the areas around the Rivers Adžina, Mavrovska, Ribnica, as well as other smaller rivers.Other important sites are the areas around the Galichnik Village.
Species with high conservation value are present on (Fig. 3A-G).
In our opinion if a better study is to be conducted, the list of species taxa will increase, and the discovery of new species for science is very likely.

Fig. 1 .
Fig. 1.Map of the studied localities in Mavrovo NP and surrounding areas.