''Unio crassus'', the thick shelled river mussel, is a
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
freshwater mussel
Freshwater bivalves are one kind of freshwater mollusc, along with freshwater snails. They are bivalves that live in fresh water as opposed to salt water, which is the main habitat type for bivalves.
The majority of species of bivalve molluscs ...
, an
aquatic bivalve mollusk
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...
in the
family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Unionidae
The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids.
The range of distribution for this family is world-wide. It is at its most divers ...
, the river mussels.
[MolluscaBase eds. (2023). MolluscaBase. Unio crassus Philipsson, 1788. Accessed through: World Register of Marine Species at: https://marinespecies.org/aphia.php?p=taxdetails&id=1044116 on 2023-01-09]
;Subspecies:
* † ''Unio crassus jaeckeli''
Modell, 1950
* † ''Unio crassus klemmi''
Modell, 1957
Ecology
As part of newly discovered reproductive behaviour, this mollusc crawls up to the edge of the water, exposing its excurrent
aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane.
An ...
, and then lets loose a stream of water. The fountain of water often contains
glochidia
The glochidium (plural glochidia) is a microscopic larval stage of some freshwater mussels, aquatic bivalve mollusks in the families Unionidae and Margaritiferidae, the river mussels and European freshwater pearl mussels.
These larvae are t ...
, and it is suggested that this spurting behavior may facilitate dispersal of mussel
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
...
e (video).
Decline
The thick shelled river mussel declined during the 20th century everywhere in
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...
due to deteriorating water quality,
habitat fragmentation and host fish limitation.
Distribution
Its native distribution is Europe and
Western Asia
Western Asia, West Asia, or Southwest Asia, is the westernmost subregion of the larger geographical region of Asia, as defined by some academics, UN bodies and other institutions. It is almost entirely a part of the Middle East, and includes Ana ...
.
* It is mentioned in annexes II and IV of
Habitats Directive
The Habitats Directive (more formally known as Council Directive 92/43/EEC on the Conservation of natural habitats and of wild fauna and flora) is a directive adopted by the European Community in 1992 as a response to the Berne Convention. The E ...
.
* Croatia
*
Czech Republic
The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...
- in Bohemia, in Moravia,
[ Horsák M., Juřičková L., Beran L., Čejka T. & Dvořák L. (2010). "Komentovaný seznam měkkýšů zjištěných ve volné přírodě České a Slovenské republiky. nnotated list of mollusc species recorded outdoors in the Czech and Slovak Republics. ''Malacologica Bohemoslovaca'', Suppl. 1: 1-37]
PDF
endangered
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...
(EN). Its conservation status in 2004-06 was unfavourable (U2) according to a report for the
European Commission
The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body ...
in accordance with the Habitats Directive.
* Finland - in southern Finland. Vulnerable.
* France
* Germany - critically endangered (''vom Aussterben bedroht'') In Germany this bivalve has disappeared from 90% of its former range.
*
Netherlands - locally extinct. In the
Netherlands
)
, anthem = ( en, "William of Nassau")
, image_map =
, map_caption =
, subdivision_type = Sovereign state
, subdivision_name = Kingdom of the Netherlands
, established_title = Before independence
, established_date = Spanish Netherl ...
it has not been seen alive after 1968 and is most likely
extinct in that country.
* Poland - endangered
* Slovakia - nearly threatened
* Sweden - very rare
* Denmark - very rare
References
External links
The Mussel Project Web Site''Fauna Europaea''
{{Commons category, Unio crassus, Thick shelled river mussel
crassus
Bivalves of Asia
Bivalves of Europe
Freshwater bivalves
Bivalves described in 1788