Shell large, globose, involute with sunken spire, smooth and polished, with very fine growth lines. Aperture which occupies the whole shell length and widens anteriorly, with outer lip uniformly curved; thickened anterior part of outer lip continuous with columella, and hence with callus on parietal wall. The soft parts can withdraw completely into the shell. Head shield large, with small eyes and four small lobes.
varies from tan or pinkish to brown and greenish grey, closely and finely mottled or speckled all over with pinkish-grey, usually with darker blotches, irregular or V shaped; occasionally with two broad indistinct bands on body whorl; interior and parietal callus are white; fresh shells covered with a thin yellowish periostracum; soft parts vary from light cream to orange.
common size :
shell rather large for the family, measuring 40-60 mm.
The common Mediterranean species, B. striata Bruguière, 1792, is smaller, more slender with a greenish-grey ground color. There is a very similar Atlantic species, B. amygdala Bruguière, 1792, which has occasionally been reported from the Canary islands, but not in the Mediterranean. The records of B. ampulla in the eastern Atlantic are misidentified with B. amygdala.
BIOLOGY / ECOLOGY
Herbivorous and nocturnal as other species of this genus, it feeds mainly on small seaweeds; can be found enclosed in a cocoon of mucus and sandgrains (Kilburn and Rippey, 1982). The spawn is a long, bright yellow to orange, tangled string of jelly, containing a continuous string of tiny oval capsules. Each one contains 1-25 eggs, which develop into free-swimming veliger larvae.
not seen alive in the Mediterranean, where only few empty shells have been found. This species lives intertidally or in shallow water, mainly in sandy mud with seagrass; in Cyprus at 9 m depth.