They were long believed to occur only in Andorra, Austria, and parts of France.

In fact, Bythinella reyniesii is probably widespread from western Germany and nearby Belgium through central and eastern France to Andorra.

[2] These are small snails, with a nearly cylindrical shell measuring just over 2 mm in length.

Thus, even though the proposed synonymy resulted from mtDNA COI and nDNA ITS1 sequence data analyses applied to the phylogenetic species concept (which does not recognize subspecies), as opposed to the morphologically diverse Bythinella bicarinata it might not even be warranted to accept the formerly distinct taxa as subspecies.

[2] The northeastern specimens formerly separated in Bythinella compressa were classified as Vulnerable (B1+2c), as they were known from less than ten freshwater springs which are affected by pollution.