Dear Elin, I hope you find it useful:

https://gq.pgi.gov.pl/article/viewFile/8287/pdf_377

Dear Elin,

there exist a couple of publications dealing with this rare bivalve species. However, regarding morphology only few are relevant.

Høpner Petersen, G., Russel, P.J.C. (1971). Caradium hauniense compared with C. exiguum and C. glaucum. Proceedings of the Malacological Society of London 39: 409-420

Høpner Petersen G. & Russell P. (1971). Cardium hauniense nov. sp. a new brackish water bivalve from the Baltic. Ophelia 9: 11-13

Høpner Petersen, C. (1958). Notes on the growth and biology of the different Cardium species in Danish brackish water areas. Meddelelser fra Danmarks Fiskeri- og Havundersgelser 2: 1-31

Additionally I have attached few own images of this species from German waters. P. hauniense is distributed in macrophyte meadows of brackish water lagoons with salinities down to around 5 psu.

Best regards

Michael

Elin:

Do look at this link for insights:

http://www.helcom.fi/Red%20List%20Species%20Information%20Sheet/HELCOM%20Red%20List%20Parvicardium%20hauniense.pdf

Best

Syed