Senegal, 43.6mm.
The « Mud-Flat Periwinkle » is an extremely variable potamidid endemic to the Atlantic coast of Africa ranging from Senegal to southern Angola. It inhabits quiet, muddy flats of intertidal brackish ecosystems especially those of mangrove swamps to about -2m deep; and is a deposit feeder that ingests mud and digests the rich organic matter contained within. It is one fo the most abundant mangrove gastropods throughout its distribution and is economically important in west Africa as it is used for food, the market demand is rather high. It is a euryhaline species capable of adapting to a wide range of salinity from 0.1 to 25mg/l. Most variable in the strength of nodules on the second spiral cord from the suture; the nominal form generally has weak nodules and the shell appear granular, whereas the form with strong nodules is known as T. f. f. radula (Linnaeus, 1758) but intermediates are also common. The specimen depicted is an exceptionally knobby specimen of T. f. f. radula, such extremes are rare. Typical shell length around 50mm., very large specimens may exceed 70mm.