Half-grooved coffee-bean snail
Shell similar in shape to M. parvulus, but sculptured below suture with 4-6 deep grooves, plus a series of shallower and more numerous grooves on base of body whorl, entire shell sometimes grooved. Inner lip with a columella pleat and two (occasionally three) sharp, widely and equally spaced parietal pleats; outer lip thin, with one spiral ridge deep inside, and usually 1 -2 additional ridges above this. Deep brown, usually heavily eroded, juvenile shells sometimes brownish-red. Animal with off-white foot and grey to black, fingerlike tentacles. Attains 1 2 mm in length.
Lagoons and estuaries of East Africa to KwaZulu-Natal (Umlalazi, Umgeni River, Durban Bay, Umkomaas, Pennington), south into Transkei, living as far down the coast as the Nxaxo River mouth. Lives on mud, mainly in the shade of mangrove trees, where submerged at high tide, often in crab holes and in crevices, down to a depth of about 1 5 cm below the surface.
In occasional juveniles the spiral sculpture develops late, but these smooth shells can easily be distinguished from M. parvulus by the parietal pleats being widely spaced and extending at least half-way up the inner lip, whereas in M. parvulus they are close to its base.