A new species of Acanthobothrium van Beneden, 1850, is described from the spiral intestine of the Japanese wobbegong, Orectolobus japonicus Regan, 1906, in the East China Sea off Magong, Taiwan. Acanthobothrium margieae n. sp. represents the first Acanthobothrium species recorded from Orectolobus japonicus and the third species of Acanthobothrium described from a host in the family Orectolobidae (i.e., the carpet sharks). Acanthobothrium margieae n. sp. is a category 8 species based on criteria set forth in a previous categorization scheme for species of Acanthobothrium and differs from all other category 8 species, and all congeners, in its extremely hyperapolytic nature. Consistent with the morphology of 2 other extremely hyperapolytic tetraphyllideans (i.e., Yorkeria saliputium Caira, Jensen, and Rajan, 2007, and Trilocularia acanthiaevulgaris Olsson, 1866), adult specimens of Acanthobothrium margieae n. sp. bear terminal proglottids in which the reproductive organs are completely undeveloped, and the anterior region of free proglottids is covered with conspicuously large spinitriches. It appears that the reproductive strategy of extremely hyperapolytic tetraphyllidean species is distinct from that seen in the more traditional hyperapolytic species in which adult worms bear terminal proglottids containing all elements of both the male and female reproductive systems. Molecular sequence data from the 28S rDNA gene were used to investigate the conspecificity of adult worms of Acanthobothrium margieae exhibiting little or no proglottid anatomy with free proglottids bearing fully mature male and female reproductive systems.