INTRODUCTION
Freshwater ecosystems, particularly rivers and streams, play a crucial role in maintaining global biodiversity and serve as sensitive indicators of water quality. Members of the phylum Mollusca – especially gastropods and bivalves – are among the most functionally and structurally essential components of lotic habitats, and they are highly responsive to environmental fluctuations (Koşal Şahin & Zeybek Yünlü 2016). The distribution and abundance of these organisms, together with their associations with physicochemical water parameters, provide valuable insights into the ecological integrity of freshwater environments (Koşal Şahin & Zeybek Yünlü 2016).
Ancylus fluviatilis (O. F. Müller, 1774), commonly referred to as a freshwater limpet, is a rheophilic gastropod typically inhabiting stony substrates in well-oxygenated streams (Koşal Şahin 2019). The species is widely distributed across Europe and the western Palaearctic region (Pfenninger et al. 2003, Albrecht et al. 2006, Richter et al. 2022); however, recent molecular studies have revealed cryptic diversity and potential taxonomic subdivisions within what has traditionally been identified as A. fluviatilis (Albrecht et al. 2006). This species exhibits a strong preference for stable, clean, and oxygen-rich habitats, making it an effective bioindicator of high-quality freshwater systems (Koşal Şahin 2019).
The Eastern Anatolia region of Turkey has been the subject of several freshwater malacological and macroinvertebrate surveys. In Tunceli Province, previous studies documented the presence of Ancylus fluviatilis within the Munzur River system (Koşal Şahin & Zeybek 2016, Gültekin et al. 2017). However, detailed locality-based records and morphometric data from the upper reaches of the Munzur River Basin remain limited. The present study provides additional locality data and shell morphometric information from the upper basin, contributing to a more refined understanding of the species’ distribution in the region.
This study provides a comprehensive morphological and morphometric assessment of Ancylus fluviatilis from the upper Munzur River Basin, eastern Turkey, supported by detailed photographic documentation of both shell and live specimens. The findings are discussed in the context of the species’ known distribution in Turkey, with emphasis on its diagnostic characters and regional occurrence patterns.
MATERIAL AND METHODS
STUDY AREA
Specimens of Ancylus fluviatilis were collected from a small tributary of the Munzur River near Ova Camping, Ovacık District, Tunceli Province, Eastern Turkey (39°21'08.6"N, 39°14'58.2"E) (elevation 1,224 m a.s.l.) (Fig. 1). The sampling site is situated approximately 38 km north of Tunceli city centre within the upper Munzur River Basin (Fig. 1). The Munzur River system originates from karstic springs in the Munzur Mountains. It is characterized by clear, cold, and fast-flowing waters with a stony substrate, typical of high-altitude mountain streams in Eastern Anatolia. During the sampling period (25–27 July 2025), water temperature ranged between 13 °C and 16 °C, with moderate flow velocity and high water transparency (Figs 2–5).
Fig. 1
Map showing the distribution of Ancylus fluviatilis in Turkey. Black dots indicate previous records, while the red star represents the new record
Figs 2–5
Habitat and microhabitat of Ancylus fluviatilis in the upper Munzur River Basin: 2 – general view of the sampling locality, including a nearby picnic and camping area; 3 – shallow stream section inhabited by the species; 4–5 – individuals attached to cobble surfaces covered by thin epilithic biofilm (held in the author’s hand)
SAMPLING AND PRESERVATION
More than 80 live individuals were collected by hand (Fig. 2) from submerged stones and cobbles in shallow sections of the tributary (5–20 cm depth). Specimens were placed in an aerated container with stream water and transported alive to the laboratory to minimize stress and shell damage. Approximately 30 individuals were preserved directly in 70% ethanol for subsequent morphological examinations. All collected material was deposited in the laboratory of the Faculty of Engineering, Şırnak University.
MORPHOMETRIC MEASUREMENTS AND IMAGING
A total of 20 shells were randomly selected for morphometric analysis to ensure representative sampling. Shell measurements were obtained using a precision digital caliper (Mitutoyo, Japan; ± 0.1 mm accuracy). Shell length (sl) (maximum anterior–posterior distance), shell width (sw) (maximum lateral distance), and shell height (sh) (maximum vertical distance from the base to the apex), aperture height (aph) and aperture width (apw) were measured following morphometric approaches commonly applied to patelliform freshwater gastropods (e.g., Pfenninger et al. 2003, Albrecht et al. 2006). Photographic documentation was conducted using a Jiusion Wi-Fi USB Digital Microscope (Jiusion Technology Ltd., China; capable of magnification ranging from 50× to 1000×). High-resolution images were used to document surface sculpture, growth lines, and overall shell morphology.
RESULTS
SHELL MORPHOLOGY
The shell of Ancylus fluviatilis is limpet-shaped and conical. Shell dimensions are given in Table 1. The apex is subcentral to slightly anterior. The shell surface exhibits fine concentric growth lines with faint radial striations (Fig. 6). Colouration is characterized by a dark grayish-brown central area gradually transitioning to a lighter yellowish margin (Figs 6–9).
Table 1
Morphometric and diagnostic morphological characteristics of Ancylus fluviatilis from Ovacık (Tunceli), Turkey (n = 20)
BODY MORPHOLOGY
The body of Ancylus fluviatilis is soft and elongate, with a well-developed muscular foot that enables strong adhesion to hard substrates (Figs 7–9). The foot is broad, muscular, and slightly oval, covering most of the ventral surface when extended. The head bears a pair of long, tapering tentacles with small black eyes located at their bases. The mantle margin is thin and translucent, extending slightly beyond the shell edge. Body colouration is generally greyish to light brown, with the head and tentacles appearing slightly darker (Figs 7–9). The soft tissues are well developed and firmly adhere to the inner shell surface, typical of rheophilic freshwater limpets.
The present study compiles previously published records and available bibliographic data on Ancylus fluviatilis from Turkey and presents a national-scale distribution map (Fig. 1). Published occurrences indicate that the species is widely distributed across different hydrographic regions of the country. In western Anatolia, it has been reported from coastal streams of İzmir, Aydın and Muğla, as well as from Gökçeada Island in the northeastern Aegean Sea (Odabaşi et al. 2019, Odabaşı 2021). Records also exist from Mount Ida (Kazdağı) in northwestern Turkey (Odabaşı & Georgiev 2014). In northwestern Anatolia, the species has been documented in streams of Kocaeli Province (Bayköse et al. 2022). Along the Black Sea region, it has been recorded from Trabzon (Kara et al. 2024) and from the Çoruh River basin and its tributaries (Gözler & Baytaşoğlu 2020). In southern Anatolia, occurrences have been reported from the Ceyhan River basin (Adana) and Mediterranean coastal drainages (Antalya) (Koşal Şahin & Zeybek Yünlü 2016, Gürlek 2019). Interior Anatolian records include major lake systems such as Lake Eğirdir and Lake Beyşehir (Yıldırım et al. 1999, Ekin 2025). Overall, the compiled data demonstrate that A. fluviatilis is distributed across western, central, and eastern Turkey, inhabiting both coastal drainages and inland freshwater systems (Fig. 1).
DISCUSSION
Previous surveys conducted in Tunceli Province documented diverse molluscan assemblages within the Munzur River Basin and confirmed the presence of the genus Ancylus in the region (Koşal Şahin & Zeybek Yünlü 2016, Gültekin et al. 2017, Koşal Şahin 2019). Within this regional framework, the present study verifies the occurrence of Ancylus fluviatilis in the Ovacık sector and provides detailed morphometric documentation supporting its identification.
The examined specimens correspond closely to the diagnostic shell morphology of A. fluviatilis as described for European and Anatolian populations (Yıldırım et al. 1999, Albrecht et al. 2006, Rıchter et al. 2022). Shell dimensions (sl: 5.8–7.6 mm; sh: 2.4–3.6 mm; sw: 4.4–6.6 mm; n = 20) fall within the size ranges reported for adult individuals, typically between 5 and 8 mm in shell length (Yıldırım et al. 1999, Pfennınger et al. 2003, Albrecht et al. 2006). Qualitative characters – including the subcentral to slightly anterior apex, fine concentric growth lines, faint radial striations and characteristic grey central pigmentation fading toward the shell margin – are likewise consistent with earlier descriptions from both Turkish and broader European material (Yıldırım et al. 1999, Albrecht et al. 2006, Koşal Şahın & Zeybek 2016, Rıchter et al. 2022, Ekın 2025).
The overall morphological conformity indicates that the Munzur specimens fall within the documented phenotypic variation of A. fluviatilis across its western Palearctic distribution (Pfenninger et al. 2003, Albrecht et al. 2006). Minor proportional differences may reflect environmental influences such as current velocity, substrate composition and mineral content, factors previously shown to affect shell form in freshwater limpets (Koşal Şahin & Zeybek Yünlü 2016, Koşal Şahın 2019).
At the national scale, available records indicate that A. fluviatilis exhibits a broadly distributed but regionally fragmented pattern across Turkish freshwater systems (Koşal Şahin & Zeybek Yünlü 2016, Koşal Şahın 2019). The species tolerates a wide altitudinal gradient and diverse hydro-morphological settings, provided that clean, well-oxygenated waters with stone- or cobble-dominated substrates are present (Albrecht et al. 2006, Koşal Şahın 2019). This ecological flexibility likely explains its occurrence in both coastal drainage systems and inland basins.
The Ovacık population inhabits a shallow (<50 cm), clear and moderately fast-flowing tributary characterized by stable cobble substrate (Figs 2–3). High water transparency and absence of dense filamentous algal growth suggest limited nutrient enrichment. Stones supporting individuals were covered by a thin epilithic biofilm composed of microscopic algae and periphyton (Figs 4–5), which represent the principal trophic resource of A. fluviatilis as a scraper grazer in lotic ecosystems (Pfennınger et al. 2003, Albrecht et al. 2006, Jungbluth et al. 2009). The combination of shallow depth, continuous flow and mineral substrate corresponds closely with the ecological profile described for rheophilic headwater populations in Europe (Albrecht et al. 2006, Jungbluth et al. 2009). The lack of excessive periphytic overgrowth further supports the interpretation of oligotrophic to slightly mesotrophic conditions.
Although the stream displays largely natural characteristics, seasonal recreational use of the surrounding area may constitute a localized anthropogenic pressure (Figs 2–3). Intensive camping activity and the use of stream water for washing activities can introduce intermittent organic inputs at microhabitat scale. Similar small-scale nutrient enrichment has been noted as a potential modifying factor in lotic gastropod habitats (Koşal Şahın 2019). Nevertheless, no abnormal periphytic proliferation or habitat degradation was observed, and individuals were well established on stable cobble surfaces (Figs 4–5), suggesting that current disturbance levels remain within the ecological tolerance range reported for the species (Albrecht et al. 2006).
Finally, it should be noted that A. fluviatilis represents a morphologically variable species complex with documented cryptic diversity across Europe (Pfennınger et al. 2003, Albrecht et al. 2006, Weıss et al. 2018). Although the present identification is supported by consistent morphological and morphometric evidence, future integrative studies incorporating molecular markers would be valuable to clarify the phylogeographic placement of the Munzur population. Concurrent measurement of key physicochemical parameters would further strengthen ecological interpretation and facilitate basin-level comparisons.
