Aquatic Mollusca  endemic to Europe

(Drawings by Fernand Angel)

First of all a piece of explanation about the fundamental difference between  "Molluscs" and "Gasteropods".

Mollusca never attack fishes, on the other hand the latter do whatever they can to eat them.  Molluscs eat fish eggs, when these do not protect them (for exemple, no tetra protects its eggs, whereas cichlids are very protective about theem).

Gasteropods are so named because of the ventral foot on which they move; in general they have a single shell.  Vegetarian and most of all omnivorous, thei use their horned tongue, named radula, to scrape and chew  their food.  This is te way they clean, by chewint it, the vegetation that covers the aquarium glass or the organic materials lying on its bottom.

Among  gasteropods, that possess lungs and do not have any operculum to close the shell opening, we mention:

Limnaea stagnalis, common in streamlets, lakes and marshes. Its shell has a heigth of  4 to 6 cm.

The glutinous limnaea, smaller, 10 to 15 mm, with a thin and transparent shell is found mostly in ditches with stagnant and calcareous water.

For more information about Limnaea click  HERE

The physa, what size is of about 1 cm, live on aquatic plants in the pure and oxygenated waters of sources, basins walls, riversides. The most known is Physa fontinalis (1) to the right, together with (2) Physa acuta

For more informatio on physa  click HERE

1)     2)

Ramshorn snail, with a flat shell, preferably live in the shallow rivers or in dormant water marshes.

For more information on ramshorn snails click  HERE

In the order of  prosobranches, that breath through gills and frequently possess a horned operculum, fixed to the dorsal part of the foot:  
The viviparous paludines (Viviparus viviparus), with a big brown greenish shell, measuring 3 to 4 cm.  These live in colonies, in the silt of slow streams or in the mud of stagnant water.

For more information on Viviparus vivparus click HERE

The bithinia (Familly of Hydrobiidae) resemble paludines, but they are smaller and the shell operculum is calcareous.  They also live in the mud or silt of marshes, where they can be found even during winter.

The valvata, which live in marshes and lakes, with a flat shell that reminds the one of ramshorn snails, may reach a size of 3 cm.  
There are also the Neritines, what shell looks like a phrygian cap and measure 8 to 9 mm and the bythinella, from sources and lakes, what shell heigth varies from 1 to 3 mm.  

Lamellibrancheous mollusca or bivalves

Lamellibranches have gills in the shape of thin blades and their shell is composed of two valves that are approximately symetric.  these are very apathic animals, that react to light by closing their valves when the light source is intercepted.  Some, like Unios and Anodontes, remain almost completely dug in into silt, and only leave out their posterior extremity that corresponds to the longer part of the shell.

Bivalves destroy algae and organic particles in suspension in the water that surrounds them, they filtrate the latter to find their food, but they also make it turbid. Furthermore, they die without any external sign and their decay becomes a pollution source for the whole aquarium.  Their positive action is therefore not that evident. Besides, the biggest species, Unios and Anodontes, are only recommended for very big volume outdoor tanks.

The main species are as follows:

The unios, or big freshwater mussels are found in the sand or in the gravel of  streamlets, lakes and shallow rivers.  Only the margaritina species must have fast moving water.  the size of these mussels varies from 8 to 15 cm.

To the right, Unio pictorum

The anodontes mostly dwell in the stagnant water of marshes and lakes.  Their size outranges Unios, reaching sometimes 12 cm shell length like Anodonta cygnea.  
The sphaerium possess an anal syphon and a breathing syphon; they usually remain in the bottom silt but sometime move under the water surface.

To the right: Sphaerium cornea (enhancement 1,5/1)

The psidium are the smallest known lamellibranches.  They differ from the former by the possession of a single anal syphon.  They move in the bottom of water, searching for decaying organisms or climb below the surface.

To the right: Pisidium amnicum (enhancement 2/1)

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