ACANTHOBOTHRIUM-NICOYAENSE N-SP (EUCESTODA, TETRAPHYLLIDEA, ONCHOBOTHRIIDAE) IN AETOBATUS-NARINARI (EUPHRASEN) (CHONDRICHTHYES, MYLIOBATIFORMES, MYLIOBATIDAE) FROM THE GULF OF NICOYA, COSTA-RICA

A new species of Acanthobothrium in Aetobatus narinari from the Gulf o f Nicoya, Costa Rica, most closely resembles Acanthobothrium colombian um in the same host and A. urotygoni in Urotrygon venezuelae from Cart agena, Colombia, by having relatively few proglottides per strobila, s pinose cephalic peduncles, bothridial margins free at their posterior ends, and irregularly shaped rather than spherical or elongate cirrus sacs. Acanthobothrium colombianum differs from the new species by bein g as much as 35 mm rather than no more than 4.7 mm long and by having 31-48 rather than 13-19 proglottides, an average of 46 rather than 15 testes per proglottis, and bothridial hooks averaging 185 mu m rather than 137 mu M in total length. Acanthobothrium urotrygoni differs from the new species by being as much as 15 mm rather than no more than 4. 7 mm long and by having V-shaped rather than H-shaped ovaries, bothrid ial hooks averaging 95 mu m rather than 137 mu m in total length, by h aving an average of 28 rather than 15 testes per proglottis, and by ha ving poral ovarian arms extending anteriorly to the posterior margin o f the cirrus sac and aporal arms extending to the lateral margin of th e cirrus sac.