Hello Alexander,

Sometime ago,I did some research with Dr Joris Koene at Vrije Universiteit (VU) Amsterdam,the Netherlands on aquatic snails specifically Lymnaea stagnalis.

He's my best bet so far on aquatic snail physiology and anatomy,get in touch with him via http://www.joriskoene.com/

Additionally,i have attached a copy of the book The classification and ecology of North American freshwater Invertebrates second edition 2001. I hope it is helpful.

Goodluck.

Hi Alexander,

I suggest contacting Peter Gloeer - he is an expert in European freshwater molluscs and maybe can help you. He is also capable of taking magnificient photos, so maybe, he alredy has some of Radix-radulae and the measurements, you are looking for (http://malaco.de/).

Best,

Fabian

Thank you so much, I try to get in contact with them.

Regards,

Alex

You might want to adjust your question a bit to focus on Lymnaea. There is a huge amount of diversity among freshwater snails, and similarly in radulae. In the species flocks of gastropods I work on in Lake Tanganyika (Lavigeria & Vinundu), for example, radular variation can be a key trait for both ecological and evolutionary studies. There is similar work on species flocks in Indonesian lakes (von Rintelen, et al), and Baikal (Sitnikova), etc. Though that said, unravelling the adaptive and non-adaptive differences can be a bit of a challenge.  And ontogenetic changes can complicate the story as well.

If the hypothesis is suggestive of different sizes and shapes among congeners, I would say that it will probably proven to be wrong or get unsufficient support. Not only due to obscurity of inter/intra-specific variation, but also to affecting drivers like habitat constraints, food choices and several abiotic factors that are not likely to be so strikingly different as the degree of the morphoplasticity in Radix. I would consider  shape rather than teeth height and with some caution radula size if I was to study biotic responses of syntopic Radix species. 

As with marine gastropods, there is a bit of variation in radular structure among freshwater gastropods.  However, if you are looking for a generality, it would appear that since most freshwater gastropods are herbivores or algal scrapers, their radulas more typically would resemble those of similarly herbivorous marine species.  The shell-drilling and flesh-tearing radulas seen often among marine predators bring in more diversity among marine groups, which of course are more diverse in other ways as well.

Sorry I answered the first question in your title, but did not see the more specific question below it.  I can't add anything on the specific question regarding Radix that has not already been answered by others above.