Belgrandiella, A. J. Wagner, 1927

Osikowski, Artur, Hofman, Sebastian, Rysiewska, Aleksandra, Sket, Boris, Prevorčnik, Simona & Falniowski, Andrzej, 2018, A case of biodiversity overestimation in the Balkan Belgrandiella A. J. Wagner, 1927 (Caenogastropoda: Hydrobiidae): molecular divergence not paralleled by high morphological variation, Journal of Natural History 52 (5 - 6), pp. 323-344 : 324-325

Taxonomy of Belgrandiella – a state of art

Belgrandiella A. J. Wagner, 1927 presents a group of minute, dioecious, caenogastropod snails, obligatory or at least facultative stygobionts, inhabiting caves and springs of southern Europe from Slovakia to the southern Balkans, and from Spain to the Caucasus and Asia Minor. However, such ‘Belgrandiella’ included nearly all the minute, not valvatiform, mostly turriform-shelled caenogastropods with a moderately high spire. Subsequent anatomical studies led to the proposal of several genera, including, Litthabitella Boeters, 1970 , Graziana Radoman, 1975 , Pontobelgrandiella Radoman, 1978 and Alzoniella Giusti and Bodon, 1984 . All of the Bulgarian ‘Belgrandiella’ belong to the genus Pontobelgrandiella , ( Rysiewska et al. 2016; Georgiev et al. 2017), the one Slovakian taxon is Alzoniella (Szarowska et al. 2011) , and none of the Greek ‘Belgrandiella’ listed by Schütt (1980) belong to this genus ( Radoman 1985; Szarowska 2006; Falniowski et al. 2012). Hence, the ‘ real ’ Belgrandiella inhabit Slovenia, northern Italy, Croatia, Bosnia and Herzegovina, as well as Austria and southern Germany ( Giusti and Pezzoli 1980; Radoman 1983, 1985; Kabat and Hershler 1993; Boeters 1998; Glöer 2002; Glöer and PeŠiĆ 2014; Falniowski and Beran 2015).

For many years all the species descriptions of Truncatelloidea were based entirely on the shell characters. Later, the anatomy of the female reproductive system as well as the morphology of the penis were considered in species descriptions (e.g. Giusti and Pezzoli 1980; Boeters 1970; 1998; Bodon 1988; Haase 1993a, 1993b, 1994; 1996; Haase et al. 2000; Glöer 2002). On the other hand, there are opinions that between the closely related representatives of the same genus, differences in anatomy are not necessarily present and, in many cases, would not be expected (e.g. Radoman 1983). The ‘ lock-and-key ’ mechanism ( Masly 2012), known mostly in arthropods, is hardly expected in molluscs, whose copulatory organs lack any sclerotised structures, and are more variable than is usually noted ( Falniowski 1987; Szarowska and Falniowski 2008; Falniowski and Szarowska 2011; Falniowski et al. 2012). Also, the anatomy of species belonging to the Belgrandiella is simplified as a result of miniaturisation and so made similar because of inevitable adaptations to osmoregulation, internal fertilisation and embryonic development inside a capsule, all necessary in a freshwater habitat. Thus, anatomical similarities are the result of parallelism, or even convergence, at least in many cases, and need not necessarily reflect common ancestry. In general, homoplasies are common in the Mollusca (e.g. Fretter and Graham 1962; Haszprunar 1988; Szarowska 2006). Notably, all the descriptions of the Balkan Belgrandiella exclude reproductive anatomy and are entirely based on the shell, whose high degree of variability has been established (e.g. Falniowski 1987; Wilke and Falniowski 2001; Falniowski and Beran 2015).

In the case of the Balkan Belgrandiella we therefore have the following information only: (1) dry shell description and photograph or drawing, and (2) type locality (if given precisely). All the other data, concerning distribution and/or variation in shell morphology, may be results of erroneous identification with a nominal species. To test the distinctness of the nominal taxa, we applied data from molecular markers: mitochondrial cytochrome oxidase subunit I (COI), nuclear histone H 3, 18S and 28S.