Champiocoiax sarae gen. et sp. nov., is an adelphohemiparasitic (hemiparasitic because it is highly pigmented) red alga collected subtidally in the Caribbean Sea of Colombia. Its hosts are three species of Champia [C. parvuia (C. Agardh) Harvey, C. salicornoides Harvey and C. compressa Harvey]. Plants are generally less than 1 mm in height and are anatomically and reproductively similar to their hosts. Champiocoiax differs from Champia in: (1) being hemiparasitic, (2) the external habit of the thallus, which is reduced and not well differentiated, (3) the cystocarps, which lack an ostiole, and (4) the monoecious gametophytes. Champiocoiax is proposed as a new genus, the first obligate algicolous ('parasitic') one for the Champiaceae (Rhodymeniales).