Laminaria japonica fucoidan is a fucan sulphate occurring in brown marine algae (Phaeophyta), typically Laminaria japonica, and has been shown to have anti-coagulant activity. The fucose content of this fucan is approx. 34.1% and it also contains galactose (approx. 4.0%), uronic acid (approx. 14.5%) and sulphate (approx. 31.7%).
A recent reference describes the properties in more detail:
Fitton H. J., Stringer D. N. and Karpiniec S. S., Therapies from Fucoidan: An Update, Marine Drugs, 13, 5920-5946 (2015)