Two new species of Echinobothrium (Cestoidea : Diphyllidea) from myliobatiform elasmobranchs in the Gulf of California, Mexico

Two new species of diphyllidean cestodes, Echinobothrium mexicanum n. sp., and Echinobothrium fautleyae n. sp., are described, the former from the spi ral intestines of the bat rays Myliobatis californicus and Myliobatis longi rostris and the latter from the spiral intestine of the cownose ray Rhinopt era steindachneri, all caught in the Gulf of California, Mexico. Echinoboth rium mexicanum is most easily distinguished from the majority of the specie s of the genus by the number of large apical hooks in each dorsoventral gro up (23) and from the remainder in the number of lateral hooklets in each gr oup on the scolex, Echinobothrium fautleyae differs conspicuously from all other members of the genus in that the first and last lateral hooklets in e ach group are distinctly larger than the other hooklets in each group. Seri al sections of the scoleces of these 2 new; species confirm that the attach ment structures on the scolex are bothria, rather than bothridia, as has be en described in other species in the genus, suggesting that the attachment structures of the scolex should be examined in more detail in the genus in general. Palmate microtriches of various forms cover the proximal bothrial surfaces of both new species and are also found on the dorsal bothrial surf aces of E. fautleyae. The distal bothrial surfaces of E. mexicanum are cove red with slender spiniform and short filiform microtriches. The cephalic pe duncles of both species possess short filiform microtriches only. Compariso n of these 2 new species with the other 3 species in this genus that have b een examined with SEM suggests that the various forms and distributions of these microtriches is unique in each of these 2 species. We believe these f eatures will prove to be taxonomically useful.