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Populations of the freshwater mussels Unio crassus and U. tumidus have declined significantly over many decades. The river Vantaanjoki, at their northern limit in southern Finland, has yielded a number of empty hinged shells of U crassus (39 shells) and U. tumidus (71 shells), which have been studied visually for taphonomical features. All of the shells are to some degree affected by taphonomical processes, particularly dissolution and fragmentation. These death assemblages of Unio shells are time-averaged as suggested by their radiocarbon (C-14) dates, with consequences for the expected temporal resolution of both death and fossil assemblages. Although the shells arc of different ontogenetic and post-mortem ages, there are no distinct differences in their preservation. Considering both taphonomical features and C-14 dating, time-averaged death assemblages, which might illustrate the time-evolving anthropogenic changes of the river environment over the last centuries, should with some caution be compared with modern populations for conservation evaluations.

This paper presents results of a malacological survey of the middle and upper section of the Jihlava River, a tributary of the Dyje River (Czech Republic). Twenty-three species of aquatic molluscs (13 gastropods, 10 bivalves) were found at 35 sites during research realised mostly in 2017 and 2020. In comparison with the lower section of the Jihlava River, a significantly lower proportion of bivalves of the family Unionidae was found in the middle and upper sections.

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)., Published as part of 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, pp. 1-64 in Zootaxa 5003 (1) on page 39, DOI: 10.11646/zootaxa.5003.1.1, http://zenodo.org/record/5120059, {"references":["Tadic, A. (1960) Najvazniji predstavnici skoljaka roda Unio iz Save, Dunava i Kopackog jezera. Prirodnjacki muzej, Beograd, 46 pp. [in Serbian]","Dokic, L. (1882) Skoljke u Srbiji. Grada za faunu Kraljecine Srbije. Kraljevsko-srpska drzavna stamparija, Beograd, 36 pp. [in Serbian]","Zivic, I., Markovic, Z. & Brajkovic, M. (2001) Macrozoobenthos in the Pusta Reka river, left tributary of the South Morava river. Archives of Biological Sciences, 53 (3 - 4), 109 - 122.","JDS-ITR National Tisza Report (2002) Report on the joint investigation of the Tisza River on the territory of the FR Yugoslavia within the international JDS-ITR Program. Federal Hydro- Meteorological Institute, Belgrade, 52 pp.","Simic, V., Simic, S., Petrovic, A., Paunovic, M., Soric, V. & Dimitrijevic, V. (2006) Biodiversity in aquatic ecosystems in Serbia (BAES ex situ online database). Faculty of Sciences, Kragujevac. Available from: http: // baes. pmf. kg. ac. rs (accessed 12 April 2015)","Novakovic, B. (2012) Indicative ecological status assessment of the Juzna Morava River based on aquatic macroinvertebrates. Water research and management, 2 (4), 45 - 50.","Savic, A. (2012) Ecological analysis of macrozoobenthos communities in the Nisava River. University of Belgrade, Belgrade, 172 pp. [PhD. Thesis, in Serbian]","Rakovic, M. (2015) Diversity of Molluscs in the Danube River (1260 - 863.5 rkm) and Taxonomic Analysis of the Genera Planorbarius, Radix, Physella and Ferrissia (Pulmonata: Basommatophora). University of Belgrade, Belgrade, 147 pp. [PhD. thesis, in Serbian]","Lucic, A., Paunovic, М., Tomovic, J., Kovacevic, S., Zoric, K., Simic, V., Atanackovic, A., Markovic, V., Kracun-Kolarevic, M., Hudina, S., Lajtner, J., Gottstein, S., Milosevic, D., Andus, S., Zganec, K., Jaklic, M., Simcic, T. & Vilenica, M. (2015) Aquatic macroinvertebrates of the Sava River. In: Milacic, R, Scancar, J. & Paunovic, M. (Eds.), The Handbook of Environmental Chemistry. Vol. 31. The Sava River. Springer, Heidelberg, New York, Dordrecht, London, pp. 335 - 359. https: // doi. org / 10.1007 / 978 - 3 - 662 - 44034 - 6 _ 13","Tomovic, J., Vrankovic, J., Zoric, K., Borkovic Mitic, S., Pavlovic, S., Saicic, Z. & Paunovic, M. (2010 b) Malakofauna of the Serbian stretch of the Danube River and studied tributaries (the Tisza, Sava and Velika Morava). In: Paunovic, M, Simonovic, P, Simic, V. & Simic, S. (Eds.), Danube in Serbia - Joint Danube survey 2. Ministry of Agriculture, Forestry and Water Management - Directorate for Water, University of Kragujevac, Faculty of Science, Institute for Biology and Ecology, University of Belgrade, Institute for Biological Research \" Sinisa Stankovic \", Belgrade, pp. 207 - 224.","Tomovic, J. (2016) Ekologija, biodiverzitet i konzervacija slatkovodnih skoljki familije Unionidae u Srbiji. Univerzitet u Kragujevcu, Kragujevac, 157 pp. [PhD. thesis, in Serbian]","Welter-Schultes, F. W. (2012) European non-marine molluscs, a guide for species identification, planet poster editions. Planet Poster Editions, Gottingen, 674 pp. [in German]","Kenderov, L. & Sashov, Y. (2017) New record of thick shelled river mussel Unio crassus (Unionidae, Bivalvia) from Palakaria river, Bulgaria. Ecological Engineering and Environment Protection, 9, 96 - 99.","Lopes-Lima, M., Kebapcy, U. & Van Damme, D. (2014 a) Unio crassus. The IUCN Red List of Threatened Species, 2014, e. T 22736 A 42465628. Available from: https: // doi. org / 10.2305 / IUCN. UK. 2014 - 1. RLTS. T 22736 A 42465628. en (accessed 11 March 2021)","Directive, H. (1992) Council Directive 92 / 43 / EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora. Official Journal of the European Union, 206, 7 - 50.","Graf, D. L. & Cummings, K. S. (2021) The Freshwater Mussels (Unionoida) of the World (and other less consequential bivalves). Available from: http: // www. mussel-project. net / (accessed 20 March 2021)"]}

The objective of this paper is to draw attention to a previously unrecognised habitat for Unio crassus Philipsson, 1788 (Bivalvia: Unionidae), namely beaver dam-and-pond complexes. The construction...

Freshwater mussels are widely used in the monitoring of pollution because they are filter-feeding, long-lived animals that tend to accumulate metals in their shells. The temporal scale of such studies can reach thousands of years, since the composition of shells preserves them against decay. This allows us to reconstruct past environmental conditions and to compare current environmental conditions to those prevalent thousands of years ago. Here we assessed metal concentrations (Ca, Cd, Cr, Cu, Fe, Hg, Ni, Pb and Zn) in recently harvested mussel shells and mussel shells found by archaeologists, and tested the hypothesis that levels of some metals are higher in today's shells, reflecting increasing anthropogenic impact. We observed lower metal concentrations (with the exception of Cd) in shells found by archaeologists (n = 35) than in recently harvested mussel shells (n = 14) (Unio crassus, Unio pictorum, Unio tumidus) in the same water bodies. There were no significant differences in metal levels among species in shells found by archaeologists, while in recently harvested mussels almost all metals for which we tested were found in their highest levels in Unio crassus. The results suggest that metal concentrations in prehistoric times were lower than today, which probably reflects human impact, rather than changes in the geochemical structure of rocks. The results also revealed that metal transfer between mussel shells and surrounding deposits does not occur. We therefore suggest that they might be successfully used as independent bioindicators.

The article substantiates the necessity of registration in the Red Data Book of Ukraine the Unio crassus Philipsson, 1788 – a mollusk, which is an indicator of water purity and an important factor of self-purification of hydro-ecosystems. As a result of monitoring studies, 300 species of Unionidae-like biotopes within all river basins of Ukraine during the period 1993-2018 have been marked with a sharp reduction of the species distribution area. Mollusk has become quite rare in the basins of the Siverskyi Donets, Dniester, Dnieper, Southern Bug, Crimea rivers, and it has not been detected at all in the hydrocenoses of the Western Bug, although in the 40-60s of the last century it was considered to be a widespread species in these regions. Its occurrence in modern reservoirs of Ukraine is only 15 %. The most common Unio crassus in the Prypiat basin (41 % occurrence) U. crassus is a rheophilic species found only in rivers. Given the overall degradation of the country’s aquatic ecosystems, the tendency to reduce the occurrence of U. crassus may intensify, which is why it is important to undertake appropriate environmental measures in a timely manner aimed at preserving the malacofauna of water basins and streams of Ukraine. In due course, this species should be listed in the Red Data Book of Ukraine with the status of “vulnerable”., У статті обґрунтовано необхідність внесення до Червоної книги України перлівниці Unio crassus – молюску, що є індикатором чистоти води та важливим чинником самоочищення гідроекосистем. У результаті моніторингових досліджень 300 типових для перлівницевих біотопів у межах усіх річкових басейнів України у період 1993-2018 рр. відмічено різке скорочення території поширення виду. Молюск став досить рідкісним у басейнах Сіверського Дінця, Дністра, Дніпра, Південного Бугу, річках Криму, а в гідроценозах Західного Бугу він взагалі не виявлений, хоча ще у 40-60-х рр. минулого століття вважався розповсюдженим видом у цих регіонах. Зустрічальність його у сучасних водоймах України становить лише 15%. Найбільш поширена перлівниця в басейні Прип’яті (зустрічальність – 41%). U. crassus – це реофільний вид, виявлений лише у річках. В умовах загальної деградації водних екосистем країни тенденція щодо зменшення зустрічальності U. crassus може посилитись, саме тому важливо вчасно провести відповідні природо- охоронні заходи, спрямовані на збереження малакофауни водойм і водотоків України. На часі внести даний вид до Червоної книги України, надавши статусу «вразливий».

We applied in vitro techniques in culturing glochidia of the thick-shelled river mussel Unio crassus, seriously threatened European species. Glochidia were freshly isolated from a gravid female. Th...

Information on the growth and age of the endangered freshwater mussel Unio crassus Philipsson, 1788 is crucial to correctly assess the conservation status of a particular population. This long-term study of individually marked specimens from four populations from central and southwest Germany revealed that zero growth and shrinkage of adult mussels from the upper 50% of their population’s length range were common phenomena. Therefore, overall shell length measurements or counting of growth lines on the shells of live adult mussels may grossly underestimate their age and should be regarded as unsuitable for determining the actual age structure of a population. Key wOrDs: growth cessation, age determination, long-term study, Unio crassus, Unionidae

Taxonomy of freshwater mussels from family Unionidae has been ambiguous for a long time. A number of methods used for their identification, including the so-called comparative method, are based on shell morphology. However, this morphology turned out to have a high level of within-species variation, and the shape of the shell of a specimen depends strongly on its environment and conditions of growth. For these reasons, the number of species recognized by the comparative method kept increasing. We applied both the comparative morphological method and methods of molecular genetics to address the taxonomy of Unionidae. We performed the comprehensive study of 70 specimens of Unionidae mussels collected from the River Ivitza, Volga basin. The specimens represented 14 comparative species, belonging to 4 comparative genera of Unionidae: Colletopterum, Pseudanodonta, Unio and Crassiana. Sequencing of the nuclear (ITS1) and mitochondrial (COI, 16S rDNA) genetic regions revealed 5 groups with high within-group genetic homogeneity separated from each other by long genetic distances. According to the comparison with the available sequences, these groups correspond to 3 Eastern European genera and 5 species: Anodonta anatina, Pseudanodonta complanata, Unio pictorum, Unio tumidus and Unio crassus. The results obtained indicate that the comparative method is inappropriate for the taxonomic analysis of East European Unionidae.

Unio crassus Philipsson in Retzius, 1788 Synonyms (in the study area) Unio musivus Spengler, 1793. Unio nana Lamarck, 1819. Unio fusculus Ziegler in Rossm��ssler, 1835. Unio irgizlaica Lindholm, 1904. Description. Shell is oval, thick (up to 8.9 mm in the anterior shell area) and moderately inflated. The ratio of shell width to its height is 0.61���0.80, and the ratio of shell height to its length is 0.46���0.62. The umbo is wide projecting considerably above the dorsal margin. Umbo sculpture is wrinkled or consists of double-looped waves and knobs. Periostracum ranges from green to dark brown, sometimes with rays from the umbo to the ventral margin. Nacre is light blue, light violet or pinkish-white. Pseudocardinal teeth are flattened relatively thick (2.5���3.0 mm) and curved. The outer and inner pseudocardinal teeth of the left valve are generally separated with similar lengths and levels of projection, but occasionally the inner is higher than the outer pseudocardinal tooth. A dark strip on the foot may be well pronounced or not. The papillae of the incurrent aperture are short, conic, and located in two rows close to each other. Comparisons. This species differs from U. pictorum and U. tumidus by having an oval shell shape, often wrinkled umbo sculpture and a higher shell height/length ratio (0.46���0.62). The labial palps in U. crassus are longer and larger than in U. pictorum and U. tumidus. The papillae of the incurrent aperture of U. crassus are shorter and arranged in two rows, whereas there are three to four rows in U. pictorum and U. tumidus. Distribution. In the Ukraine and European Russia restricted to the Black, Caspian and Baltic Sea basins, also found in a restricted range in Transbaikalia, Asian Russia (Fig. 1)., Published as part of Klishko, Olga, Lopes-Lima, Manuel, Froufe, Elsa, Bogan, Arthur, Vasiliev, Lyudmila & Yanovich, Lyudmila, 2017, Taxonomic reassessment of the freshwater mussel genus Unio (Bivalvia: Unionidae) in Russia and Ukraine based on morphological and molecular data, pp. 93-112 in Zootaxa 4286 (1) on page 109, DOI: 10.11646/zootaxa.4286.1.4, http://zenodo.org/record/828332, {"references":["Retzius, A. J. (1788) Dissertatio historico-naturalis sistens nova testaceorum genera. Quam venia ampliss. Facult. Philosophicae Praeside D. M. Andr. J. Retzio [= A. J. Retzius], ad publicum examen defert laurentius Munter Philipsson Scanus. Ad diem X. Decembris 1788. Typis Berlingianis, Lundae, 23 pp.","Spengler, L. (1793) Beskrivekse over et nyt Slaegt af de toskallede Konkylier forhen af migkaldet Chaena, saa der Linneiske Slaegt Mya, hvilket noire bestemmes, og inddeles i tvende Slaegter. Skrivter af Naturhistorie-Selskabet, KiObenhavn, 3 (1), 16 - 69, pl. 2.","Lamarck, J. - B. M. (1819) Histoire Naturelle des Animaux Sans Vertebres. Vol. 6. Imprimerie de A. Belin, Paris, 343 pp.","Rossmassler, E. (1835) Iconographie der Land- und Susswasser-Mollusken, mit vorzuglicher Berucksichtigung der europaischen noch nicht abgebildeten Arten. 1 (1 & 1). Arnoldische Buchhandlung, Dresden und Leipzig, 132 & 26 pp.","Lindholm, W. (1904) Zur Molluskenfauna der Governements Kursk und Orenburg. Annual Report of Zoological Museum of Imperial Academy of Sciences, 8, 338 - 344."]}