Ascophyllum fucoidan is a fucan sulphate occurring in brown marine algae (Phaeophyta), typically Ascophyllum nodosum, and has been shown to have anti-coagulant activity. Other therapeutic indications are reported in the literature.
Reference:
Fitton H. J., Stringer D. N. and Karpiniec S. S., Therapies from Fucoidan: An Update, Marine Drugs, 13, 5920-5946 (2015)