Structure of sulfated α-L-fucans (SFs) from (A) the sea urchin Lytechinus variegatus (LvSF), and sea cucumbers (B) Isostichopus badionotus (IbSF) and (C) Holothuria floridana (HfSF). They are composed of 3-linked α-L-fucose units with 2- and/or 4- sulfation substitutions within repeating tetrasaccharide building blocks. The four types of fucose units are indicated by the letters A-D in each structure. The sulfation patterns of these SFs are (A) [2,4-2-2-4]n, (B) [2,4-2-2-0]n, and (C) [2,4-0-2-2]n.