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Species spotlight XI

Mercuria cf. similis (Draparnaud, 1805)
Xlendi, Gozo

The family Hydrobiidae is a large group of small snails with gills (not lungs) living in aquatic habitats, predominantly fresh and brackish. Four representatives are found in the Maltese Islands, the largest of which is the freshwater Mercuria cf. similis (Draparnaud, 1805)*. As a denizen of fresh water bodies, usually close to Blue Clay substrates, Mercuria is rare in Malta but rather more frequent in Gozo. Colonies graze microscopic algae growing on submerged or perennially wet overhangs, and seem to prefer running, clear water. The blue-greyish shell, large shell size and habitat distinguishes it from a similar species, Pseudamnicola moussonii (Calcara, 1841), which will be discussed in a future post.

*In taxonomy, a 'cf.' indicates uncertainty in assigning a specific epithet to a specimen. The uncertainty in this case derives from anatomical differences between Maltese Mercuria and other populations of M. similis.

Mġarr, Gozo

Species spotlight X

Many members of the family Ferussaciidae tend to adopt subterranean or cavernicolous lifestyles. One such species may be found living in areas of clayey soil along the cliffs and beaches of Mellieħa; this is the small and elusive Hohenwartiana hohenwarti (Rossmässler, 1839), which at first glance resembles its relative Ferussacia folliculum (Gmelin, 1791).

Hohenwartiana hohenwarti (Rossmässler, 1839)
Għajn Tuffieħa, Malta

In contrast to Ferussacia, however, the elongated shell of Hohenwartiana is light and thin enough to render the internal organs clearly visible. The streamlined shape allows the animal to easily navigate around the clay fragments in which it lives. After the death of the animal, the shell turns an opaque white and disintegrates relatively quickly.

The specimen above was retrieved from clay for photographic purposes and replaced quickly. My hand in the background gives an idea of the specimen's size.

It's a snail's life...

Click on image for a larger view.

Species spotlight IX

Tudorella melitense (Sowerby, 1847)
Xlendi, Gozo

Tudorella melitense (Sowerby, 1847) is the only snail with an operculum ('door') which is native to the Maltese Islands. Under a 'biological species definition' it may be considered to be a local variety of Tudorella sulcata (Draparnaud, 1805), which also occurs in Sicily; Pfenninger et al. (2010)*, in their work on the DNA of Tudorella, consider it a lineage which is only found in the Maltese Islands.

Għajn Tuffieħa, Malta

The shell is very variable, and may be orange, white or purple, with or without bands.

Għajn Tuffieħa, Malta

*Pfenninger, M., Véla, E., Jesse, R., Arantzazu Elejalde, M., Liberto, F., Magnin, F., Martínez-Ortí, A., 2010. Temporal speciation pattern in the western Mediterranean genus Tudorella P. Fischer, 1885 (Gastropoda, Pomatiidae) supports the Tyrrhenian vicariance hypothesis. Molecular Phylogenetics and Evolution, 54: 427-436.