Two new species of Acanthobothrium Beneden, 1849 (Tetraphyllidea : Onchobothriidae) from horn sharks in the Gulf of California, Mexico

Between 1993 and 1996, 26 individuals of two species of horn sharks were co llected from the upper Gulf of California and their spiral intestines exami ned for onchobothriid tapeworms. Heterodontus francisci was found to host A canthobothrium puertecitense n. sp. Based on the criteria of Ghoshroy & Cai ra (2001), this is a Category 4 species (with >15mm total length, >50 progl ottids, >80 testes and a symmetrical ovary). It differs from the four Categ ory 4 species previously reported from either the western Atlantic or easte rn Pacific Oceans, including A. bajaense (emend.) which was described from H. francisci, in hook-shape, total length, number of proglottids, number of testes and number of columns of vitelline follicles. H. mexicanus was foun d to host Acanthobothrium santarosaliense n. sp., which, based on the crite ria of Ghoshroy & Caira (2001) is a Category 3 species (with >15mm total le ngth, >50 proglottids, > 80 testes and an asymmetrical ovary). A. santarosa liense differs from the five Category 3 species previously reported from ei ther the western Atlantic or eastern Pacific Oceans in its size, euapolytic nature, lack of dark matrix from the bases of the hooks, hook-shape, and d istribution and number of testes. In addition to the difference in ovarian symmetry, A. puertecitense possesses fewer testes, fewer proglottids, is a shorter worm, possesses a more anterior genital pore and vitelline follicle s which extend further forward anteriorly than in A. santarosaliense. This represents the first report of onchobothriids from H. mexicanus and the fir st report of onchobothriids from H. francisci in the Gulf of California. Th e apparent host-specificity of both new species should be viewed with cauti on until a greater sample of host individuals of both species can be examin ed. The fact that both new tapeworm species are known only from the Gulf is also considered to be a preliminary result, given the small sample of host individuals examined from these regions to date. This brings the total num ber of species of Heterodontus known to host Acanthobothrium to four and th e total number of Acanthobothrium species described from heterodontiform sh arks to five.