Hyperapolytic species of Acanthobothrium (Cestoda: Onchoproteocephalidea) from batoids off Argentina

Two hyperapolytic species of Acanthobothrium Blanchard, 1848 have been collected from Discopyge tschudii Heckel, 1846 and Zapteryx brevirostris (Müller et Henle) along the coast of Argentina. Acanthobothrium stefaniae sp. n. from D. tschudii is a category one species (i.e., it is less than 15 mm in total length, possesses fewer than 50 proglottids, fewer than 80 testes and essentially symmetrical ovary), and differs from all congeners by the following combination of features: proglottid hyperapolysis, hook morphology, size and shape of the cirrus sac, and by having spinitriches in the distal bothridial surface. This is the first record of Acanthobothrium in Discopyge Heckel, 1846. The specimens from Z. brevirostris conform to the morphology of Acanthobothrium zapterycum Ostrowski de Núñez, 1971. A redescription of this species is presented, which expands most ranges of measurements originally given, and provides details omitted in the original description, including the microthrix pattern. This study allowed us to observe the intraspecific variation in ovarian symmetry in A. zapterycum, which shed some doubt on the validity of this as a diagnostic feature. The reproductive strategy (apolysis) of several species of Acanthobothrium was reviewed and summarized.