Planaxis sulcatusPlanaxis sulcatus, common name the tropical periwinkle, is a species of sea snail, a marine gastropod mollusc in the family Planaxidae.DistributionThis marine species occurs in the Red Sea and in the Indian Ocean off Mozambique, Kenya, Madagascar, Tanzania and off Mauritius, Chagos, Aldabra and the Mascarene Basin. It is also found off the Pakistani coast, specially Sonmiani Bay.DescriptionThe size of the shell varies between 13 mm and 35 mm.EcologyParasites of Planaxis sulcatus include trematode Lobatostoma manteri.