The Hydrobiinae: North Atlantic Mud-snails

The fine-looking animal above (photographed by Roy Anderson) is Hydrobia acuta neglecta, a member of the subfamily Hydrobiinae of the family Hydrobiidae. Most members of the Hydrobiidae are freshwater snails (another hydrobiid has been covered on this site here), but Hydrobia and genera closely related to it are found in brackish or marine environments. They are grazers on algae and detritus, and can be very abundant. The group is found in coastal, muddy regions on either side of the North Atlantic, extending on the European side through the Mediterranean and into the Black Sea. Hydrobiids as a whole are not well-studied animals, mostly for one ultimate reason: they're really tiny. Most hydrobiids are only a few millimetres in length. And coupled with that small size is a strong conservatism in external appearance. Compare Hydrobia acuta neglecta above with another hydrobiine, Ecrobia ventrosa, also photographed by Roy Anderson:

The external shell of a hydrobiid supplies few details to distinguish and classify taxa, and dissecting out a snail that small to examine its soft parts is no cake-walk.

Monophyly of the saltwater hydrobiids is supported by molecular data (Wilke et al. 2013), and they form the core of the Hydrobiinae. Bouchet et al. (2005) also listed the family-group taxa 'Pyrgorientaliinae' and 'Pseudocaspiidae' as synonyms of Hydrobiinae. These were both established for freshwater species: the Pyrgorientaliinae for two genera from Turkey, and Pseudocaspiidae for two genera from central Asia (Kabat & Hershler 1993). Whether these taxa are truly associated with the hydrobiines, I suspect, requires further investigation (it should also be noted that many other authors have used 'Hydrobiinae' to refer to more extensive groupings included taxa listed by Bouchet et al. as separate subfamilies).

REFERENCES

Bouchet, P., J.-P. Rocroi, J. Frýda, B. Hausdorf, W. Ponder, Á. Valdés & A. Warén. 2005. Classification and nomenclator of gastropod families. Malacologia 47 (1-2): 1-397.

Kabat, A. R., & R. Hershler. 1993. The prosobranch snail family Hydrobiidae (Gastropoda: Rissooidea): review of classification and supraspecific taxa. Smithsonian Contributions to Zoology 547: 1-94.

Wilke, T., M. Haase, R. Hershler, H.-P. Liu, B. Misof & W. Ponder. 2013. Pushing short DNA fragments to the limit: phylogenetic relationships of ‘hydrobioid’ gastropods (Caenogastropoda: Rissooidea). Molecular Phylogenetics and Evolution 66 (3): 715-736.