A NEW SPECIES OF ACANTHOBOTHRIUM VAN-BENEDEN, 1849 (CESTODA, TETRAPHYLLIDEA) FROM RIORAJA-CASTELNAUI (CHONDRICHTHYES, RAJOIDEI) IN COASTAL WATERS OF ARGENTINA

Acanthobothrium marplatensis n. sp. is described from the spiral intes tine of the skate Rioraja castelinaui taken off Mar del Plata, Argenti na. The new species is compared with those species that it most closel y resembles morphologically, to species reported from other skate host s and to species described from the same geographical region. A. marpl atensis is most similar to A. paulum, A. benedeni, A. costarricense, A . fogeli, A. himanturi, A. lintoni, A. monksi, A. olseni, A. puntarena sense and A. mathiasi. All of these species share a similar combinatio n of characters (12-40 proglottids, 20-50 testes and total length of 2 -10 mm). A. marplatensis can be differentiated from these species and those described from skates by a combination of the following characte rs: 4.79-8.44 (6.18) mm long, with 18-30 (24) proglottids, spinose cep halic peduncle 160-338 (227) long, bothridial hooks with total length 93-134 (115), 24-39 (32) testes per proglottid, cirrus-sac curved ante riorly, ovarian lobes never reaching the level of the cirrus-sac and v aginal sphincter absent. Geographically, the new species can be distin guished from A. zapterycum and three different species designated as ' 'Acanthobothrium sp.'' reported from the coast of Uruguay and Argentin a by the size of the worms, number of proglottids, position of the gen ital pores and size of the bothridial hooks. A. marplatensis showed th e greatest preference for chambers 2 and 3 of the eight chambers of th e spiral intestine. The mean intensity of infection in individual host s increased with host size and was greater in spring and summer than i n cold seasons. The intensity of infection was unrelated to host sex.