1. Theodoxus danubialis (C. Pfeiffer, 1828)

Findings in Serbia.

Nerita danubialis var. carinata: Clessin (1887).

Theodoxus danubialis carinatus: Ehrmann (1933); Zilch & Jaeckel (1962); Karaman & Karaman (2007).

Neritina stragulata: Möllendorff (1873).

Neritina danubialis var. stragulata: Clessin (1887).

Theodoxus danubialis var. stragulata: Grossu (1956).

Theodoxus danubialis stragulata: Karaman & Karaman (2007).

Theodoxus danubialis: Hesse (1929); Ehrmann (1933); Jaeckel et al. (1958); Matoničkin et al. (1975); Frank et al. (1990); Arambašić (1994); Jovanović (1990); Karaman (2001); (2012); Simić & Simić (2004); Jakovčev-Todorović et al. (2005); Živić et al. (2005, 2006); Csányi & Paunović (2006); Jović et al. (2006); Karaman & Karaman (2007); Paunović et al. (2007a, 2008, 2012 a); Marković et al. (2012, 2014); Novaković (2012); Martinović-Vitanović et al. (2013); Tomović et al. (2014); Savić et al. (2016); Živić (2020); Gojšina (2021 pers. comm.).

Common name. Danube nerite.

Morphology. Medium-sized species (shell up to 15 mm). Shell is oval shaped and brightly coloured, usually with dark zigzag pattern. Sometimes shell colouring can be uniformly black. Operculum is yellowish, with apophysis and pseudoapophysis. For more details see Glöer (2019: 40, figs 24, 25).

Distribution and ecology. Species native to the Danube basin, found in northern Italy as well. The snail prefers hard substrate of large and medium-sized rivers at lower attitudes (Welter-Schultes 2012; Marković et al. 2014). In Serbia, the most numerous populations are found in the Danube and Sava Rivers tributaries such as Drina, Velika Morava, Mlava, Nišava and Timok Rivers.

Other remarks. The spread of competitive alien and invasive species in the 21 ^st century, alongside with general habitats deterioration, could be the main cause of decreasing population trends of this species. The snail is considered as critically endangered in northern parts of its distribution area (Germany, Austria, Czech Republic) (Welter-Schultes, 2012). The species has LC status on the IUCN Red List (Tomović et al. 2010).