Distribution: Eurasia: hypothesized as native in most Europe, naturally absent only in Ireland, Scandinavia north of 61°30'N, eastern Adriatic basin and western and southern Greece where it is now introduced. In Asia, native eastward to western Yenisei drainage south of 60° N. Introduced elsewhere.

How to read the map

The literature species report in a country is represented by an icon (a circle) in the middle of the country polygon.
Important: a report in the literature does not necessarily mean that the species is currently present in the country! There are errors in literature, misidentifications, and some species have been locally or globally extirpated or eradicated.

The patterns and colours of the icon give 4 additional indications (see the legend under the map for the signification of the different colours and patterns):

• Presence status: the colour of the ring (green: Present; orange: Possible; red: Absent)
• Introduction status: a white 'i' in the middle of the circle indicates that the species has been introduced, if the presence ring is green it means that the species established itself or that we don't know the current presence status, if the presence ring is red it means that the species did not established itself.
• Threat status: the pattern of the ring (not dashed: not threatened or no information; dashed: any status indicating that the species has a national threatened).
  Important: This is the national threatened status, not the global IUCN one.
• Salinity status = milieu: the colours in the middle circle (blue: Marine; green: Brackish; light blue: freshwater; dark green: Land).

How to interpret the map

• The icon in a country polygon indicates that the species has been reported at least once in the country, BUT NOT NECESSARILY that it is present IN THE ENTIRE COUNTRY.
• It is particularly the case for large country such as Brazil, USA, Canada, Russia, China, India, Indonesia, Australia, etc.
• For example, a number of freshwater species present in western European countries are also present in the western part of Russia, but not beyond the Ural mountains. Still the icon for Russia is placed in its Asian part.
• The icon is placed approximately in the middle of the country, even for the species that are marine only.
• For marine species, it does not mean either that the species is present in all oceanic coasts of the countries (e.g., Altlantic and Pacific for USA and Canada).
• So the map needs to be interpreted carefully, but we think it helps to give a quick view of the distribution by country, in a better way than the textual list of countries when it is over a dozen countries.

The map in this page was supported by BioFresh that has received funding from the
European Union's Seventh Programme for research, technological development and demonstration under grant agreement No 226874