Between Sep 1982 and May 1983 the life cycles of Acoelomorpha and Platyhelminthes were studied in a sheep-grazed supratidal salt marsh on the island of Sylt. Based on monthly sampling, each individual was determined to species level and its body length measured (to the next 50 µm in individuals < 0.5 mm, otherwise to the nearest 100 µm). Sexual maturity was estimated separately for male and female organs using a 6-step scale: (0) juvenile, no sign of sexual organs; (1) early adolescent, bright patches appear as first sexual organs start to develop; (2) adolescent, bright patches for all organs visible; (3) late adolescent, beginning production of sperm or eggs; (4) sexually mature; (5) decline stage. Most species had a life span of 1 year with a single reproductive period in winter.