ECHINOBOTHRIUM-MEGACANTHUM SP. N. (CESTODA, DIPHYLLIDEA) FROM THE EAGLE RAP MYLIOBATIS-GOODEI (CHONDRICHTHYES, RAJOIDEI) FROM THE PATAGONIAN SHELF OF ARGENTINA

A new species of Echinobothrium is described from the spiral intestine of the eagle ray Myliobatis goodei Garman, 1885 from the San Matias G ulf, Argentina. Echinobothrium megacanthum sp. n. is distinguished fro m all others by the following combination of characters: 27 large hook s per apical group, a continuous row of 12 hooklets on each lateral su rface of the rostellum, 38-43 spines per row on the cephalic peduncle and 13-15 testes per segment. The new species is most similar to E. eu zeti Campbell et Carvajal, 1980, E. mathiasi Euzet, 1951 and E. raschi i Campbell et Andrade, 1997. Echinobothrium megacanthum can be differe ntiated from E. euzeti by the number of spines per row on the cephalic peduncle (100-107 in E. euzeti), number of lateral hooklets (6-7), an d number of testes (37-42). It can be distinguished from E. mathiasi b y the number of lateral hooklets (4 in E. mathiasi), number of spines per row on the cephalic peduncle (50-60), number of testes (25-30), an d from E. raschii by the number of lateral hooklets (27-36 in E. rasch ii), number of spines per row on the cephalic peduncle (21-26), and nu mber of testes (17-23). Differences in the scolex armature clearly dis tinguish E. megacanthum from E. pigmentatum Ostrowski de Nunez, 1971, E. acanthocolle Wojciechowska, 1991 and E. notoguidoi Ivanov, 1997, th e only species described previously from hosts in the southwestern Atl antic. Echinobothrium pigmentatum differs in possessing 20 large apica l hooks, a continuous row of 21-22 lateral hooklets and 9-13 spines on the cephalic peduncle. The scolex armature of E. acanthocolle lacks l ateral hooklets, and possesses only 5 spines per row on the cephalic p eduncle. Echinobothrium notoguidoi differs in the possession of a wide corona of spines posterior to the rostellum, number of spines per row on the cephalic peduncle (24-26), number of hooklets disposed in late ral groups (13 per group), and number of large apical hooks (31).