Retusa truncatula
Habitat: it lives in the infralittoral zone in a sandy habitat.
Distribution: it can be found all over the Mediterranean. We think it is the most common species of its genus.
Notes: species cylindrical in form, a little bit narrower in upper half of whorl. It is more or less enlarged in the lower part. Upper part is almost always flat-sided and generally apex is not visible but, as per photo, specimens with apex protruding from spiral (Oliverio & Tringali, 2001) are rarely found. Sculpture is made by vertical striae vanishing in the lower part of spiral. There are often present 2-3 transparent streaks showing up on a ground dominant white in colour. In apical part there are visible 22-25 helicoidal plicae originating axial sculpture. Aperture runs parallel to columella, then it enlarges in the lower part originating a mouth roundish in form where it is present a slight columellar plica. There are many synonyms assigned to this species, particularly we remind R. semisulcata (Philippi, 1836) where, as shown by Tringali (1995), there are present all forms of transition to go back to a unique entity. At present another species considered doubtfully as synonym of truncatula is R. dilatata Pallary, 1904, pointed out along Tunisia coasts, which has a greater enlargment in the lower part of spiral and longitudinal ribs present in the lower part of whorls too. Average measures of adult specimens reach 3.5 mm in height.