Liostomia G.O. Sars, 1878

Type species, by subsequent designation: Turbonilla clavula Lovén, 1846; designated by Monterosato 1884:95. Western Sweden (Bohuslän).

Pyramidellids with cylindrical to slightly conical shells, with short to moderately long whorls. Outer lip of aperture almost straight, parallell to the main axis. No spiral sculpture. No columellar fold. Umbilicus present, may be deep and spacious. Protoconch intorted, completely immersed in the first teleoconch whorl. Second teleoconch whorl usually <350 µm high. Operculum light horncoloured, thin and translucent with a small, excentric spire, and no ‘anchor’ or internal process (see G.O. Sars, 1878, Figure 39).

This is seen as a polyphyletic group which was already pointed out by G.O. Sars. He erected the genus for two species which he found to be very similar to Odostomia, but which did not have a columellar fold and possessed a thin earshaped operculum. Except for these characteristics, the two species had very little in common. Monterosato (1884) designated Turbonilla clavula Lovén, 1846 as genotype, while Dall & Bartsch (1904) happened to choose Rissoa eburnea Stimpson, 1851. The taxonomic status has been disputed by later workers. Van Aartsen (1987) regards it as part of Odostomia s.s., while Fretter et al. (1986) treat it as a separate genus. Formally (e.g. Thiele 1929) it was seen as a subgenus of Menestho Møller, 1842. Warén (1991) reviewed the group and expanded it to include four species.

Key to the species of Liostomia, based on shell morphology

1a. Shell conical and turriculate with tumid whorls ......................... Liostomia eburnea

1b. Shell more or less cylindrical with flattened whorls ......2

2a. Shell narrow cylindrical, with smooth, shiny, unblemished surface ............................ Liostomia clavula

2b. Shell slightly conical, often with corrosion marks .........3

3a. Shell around 1.6-1.7 mm long with four whorls ............................. Liostomia afzelii

3b. Shell larger, around 2.25 mm long with four whorls, deep and channeled suture .................. Liostomia hansgei