Shell solid, usually globose but changeable in form, whorls smooth and convex crossed by fine growth striae only, apex sharp. Last whorl very large, suture linear and clear, semicircular in aperture, columella arched, callous, quite clear, usually bright dark brown in colour, external lip sharp, internally brown in colour. Usually greyish, but, very often, also either black or brownish in colour, with one darker band in the middle of the last whorl. Operculum corneous, dark brown in colour. It closes its aperture hermetically to retain a few water inside during the long dry periods. Usually yuvenile forms have a lighter colour pattern but they maintain the adult specimens outline. It feeds on algae. During Spring it releases egg capsules dispersing them at high tide. The adult specimens average measures are around 5-7 mm in height.

Diagnostic characters
Shell with flexible periostracal flap along outer lip, of which the origin is tangential to the last whorl. Surface smooth, whorls only slightly tumid and sutures shallow. Outer lip everted at base of columella. Dark bluish or brownish black, spire usually eroded to fawn. Tentacles with only longitudinal black lines. Penial glands in more than one row. Oviparous, female duct glandular.
Other characters
The shell is solid, the spire with a nearly straight profile. Growth lines are present, sometimes wrinkling the surface of the whorls. The aperture is pointed at its apical end. Though the general appearance suggests no colour pattern there is often a white spiral band on the base of the shell and a dark one round the periphery of the last whorl; dark and light stripes may also run across this whorl. Up to 9 mm high, 7mm broad; last whorl occupies about three quarters of the shell height, the aperture more than half.
The animal is in general like L. littorea. The ovipositor is linked to the female opening by a ciliated groove. The body is grey with dark lines along the tentacles, white round each eye and on the sole of the foot.
In most places on British and Irish coasts where it occurs L. neritoides is the highest of the Littorina species. It is to be found in cracks in. and on the surface of, rocks from the Pelvetia level to heights determined by exposure: the higher the splash zone the higher the winkles can survive. Sometimes they are encountered as low as M.H.W.N.T. (Moyse & Nelson-Smith, 1963) and this is usually explained as due to high humidity or to a downward breeding migration. Their food is predominantly black lichens (Daguzan, 1976a), but they also eat detritus. They are found on all coasts except in the southern half of the North Sea, where suitable habitats are absent; they are, however, local and are often not present even where condi¬tions seem suitable. Outside the British Isles L. neritoides has been recorded from Scandinavia to the Mediterranean and Black Seas.
Breeding occurs from autumn to spring, each egg being laid in a disk-shaped capsule shed into the plankton (Lebour, 1935c); this may be achieved by the downward migration referred to above, but capsules may be deposited in pools at the level at which the adults live. Veliger larvae hatch from the capsules and spend about three weeks in the plankton before settling at a much lower level on the shore than their final home, which is reached by upward migration (Fretter & Manly, 1977a). Breeding rates are very variable and many animals apparently fail to reproduce in any given year, perhaps depending on weather conditions (Hughes & Roberts, 1980). The rate of growth, for the same reasons, is equally variable, but animals with shells 7 mm high are probably about five years old (Lysaght, 1941; Hughes & Roberts, 1980).

Shell small in sizes, globose, conic, surface smooth, bright. There are visible only thin growth striae. Whorls convex, suture broad. Last whorl, quite inflated, is about % of total height. Aperture oval in form, peristome continuous, columella arched and callous. Umbilicus almost covered by callous deposit. Uniform yellow-brown in colour, sometimes very light, almost white in colour (variant pallida Jeffreys). Basic difference from L. sicana is due to sizes of protoconch that, as far as this last one is concerned, has a nucleus small, roundish, protuberant, while as far as M. neritoides is concerned, it is wider and less protuberant. Juvenile specimens have umbilicus opener but they are quite recognizable from sicana owing to protoconch sizes. Average measures of adult specimens are around 2.5 mm in height.

Really common all over the Mediterranean where it makes quite numerous colonies. It lives adherent to rocks, into cliff pools and into rock crevices in the emersed zone. It has a high resistance and it lives without water for a long time.