Mastocarpus papillatus

Mastocarpus papillatus, sometimes called Turkish washcloth, black tar spot, or grapestone is a species of red algae in the family Phyllophoraceae. It is sometimes confused with the distantly related Turkish towel (Chondracanthus exasperatus) which is of a similar texture but larger. The specific epithet papillatus ('with papillae') is due to the nipple-like projections on the female gametophyte which can give the texture of a terrycloth washcloth found at a Turkish bath.