Diagnostic characters
Shell delicate, somewhat globular with hardly any spire (apical angle 150°), the last whorl very large. Aperture expanded and D-shaped. Columellar groove very broad and umbilicus wide. Greenish.
Other characters
The shell has 3-4 rapidly expanding whorls the last of which constitutes most of its bulk. Female shells may grow to a height of 12 mm and a breadth of 6 mm, whereas male shells are only half that size. The last whorl occupies nearly the whole of the shell height, the aperture 80-85%.
The animal is like that of other species. White, with grey on the sides of the foot.
L. pallidula is found on the same type of shore as other Lacuna species, on weeds, almost always Fucus serratus, at L.W.S.T. and to depths of 70 m (Smith, 1973). It is widespread in the British Isles and occurs in Europe from France to the Arctic as well as in Greenland and south to Connecticut. Breeding may occur throughout the year but is maximal February to May. Eggs are laid in jelly masses on the fronds of Fucus serratus; each mass contains a variable number of eggs (15-113), each in its own capsule. The mass is oval or circular, not kidney-shaped, in outline, slightly domed and tightly fastened to the substratum. In it the egg capsules lie in rough concentric rings, pressed together so that their outlines are angular (Goodwin. 1979). Development is direct and young snails emerge. They grow rapidly from May to October; thereafter the rate of growth of the sexes differs: females grow by 0.91 mm shell height per month from October until February then by 0.27 mm per month; males grow slowly and so reach a much smaller final height than females. Growth slows abruptly at spawning, and all the snails are dead by June or July (Smith, 1973).