Unio crassus Philipsson, 1788

Marković, Vanja, Gojšina, Vukašin, Novaković, Boris, Božanić, Milenka, Stojanović, Katarina, Karan-Žnidaršič, Tamara & Živić, Ivana, 2021, The freshwater molluscs of Serbia: Annotated checklist with remarks on distribution and protection status, Zootaxa 5003 (1), pp. 1-64 : 39

82. Unio crassus Philipsson, 1788

Findings in Serbia.

Unio stevenianus: Tadić (1960) .

Unio dokici: Tadić (1960) .

Unio piscinalis: Droüet (1881, 1884); Tadić (1960).

Unio cytherea: Droüet (1881, 1884); Dokić (1882); Tadić (1960).

Unio crassus: Dokić (1882) ; Tadić (1960); Marković (1999); Živić et al. (2001); JDS-ITR Report (2002); Simić et al. (2006); Novaković (2012, pers. comm. 2012, 2014, 2018); Savić (2012); Raković (2015); Lucić et al. (2015); Tomović et al. (2010 b); Tomović (2016).

Common name. Thick shelled river mussel.

Morphology. Large bivalve. Shell is distinctly rounded in the posterior end, with a completely rounded dorsal margin. It reaches 70 mm (rarely up to 120 mm) in length, 45 mm in height and 35 mm in depth. For more details see Welter-Schultes (2012: 12, figure on the top of the page).

Distribution and ecology. Western Palearctic species preferring clean waters (rivers and smaller watercourses) in lowland regions. It usually could be found on a sandy or stony substrate, avoiding polluted muddy rivers. In Serbia it has been found in the Sava, Tisza, Velika and Zapadna Morava, Nišava and Kolubara Rivers and catchments. There are also sporadic findings of the species in the Danube River ( Tadić 1960; Tomović et al. 2016). This mussel rarely reaches altitudes over 300 m. a.s.l. in Serbia, while in the neighboring Bulgaria, for example, an abundant population has been recorded as high as nearly 900 m. a.s.l. ( Kenderov & Sashov 2017).

Other remarks. Despite its relatively wide distribution range it is one of Europe’s most endangered freshwater mussel taxa, being assessed as EN on the IUCN Red List ( Lopes-Lima et al. 2014 a) and listed in the 92/43 EEC Directive (annexes II and IV; Directive, 1992). The species is protected on national level as well by Serbian national regulative (Annex 1-strictly protected species; Official Gazette of RS 5/2010, 47/2011, 32/2016, 98/2016). One of the limiting ecological factors for this species are juveniles, which are extremely sensitive to any pollution and require well-oxygenated waters ( Welter-Schultes 2012). There are 318 nominal species as synonyms ( Graf & Cummings 2021).