A new Orygmatobothrium Diesing, 1863 (Eucestoda, Tetraphyllidea) parasite of Mustelus schmitti Springer, 1939 (Carcharhiniformes, Triakidae) from the southwestern Atlantic Ocean Author Suriano, Delia Mabel Author Labriola, Juliana Beatriz Helmintología. Estación Costera, Departamento de Ciencias Marinas, de Ciencias Exactas y Naturales, Universidad Nacional de Mar del plata, Dean Funes 3350 (7600) Mar del Plata (Argentina) dsuriano @ mdp. edu. ar .. dsuriano@mdp.edu.ar text Zoosystema 2001 23 4 669 674 journal article 10.5281/zenodo.5754730 1638-9387 5754730 Orygmatobothrium schmittii n. sp. ( Fig. 1 ) TYPE MATERIAL . — Holotype ( Museo Argentino de Ciencias Naturales Bernardino Rivadavia , Helminthological Collection 382/1-2); paratype ( MNHN 20 HG, 2 slides 158 CIX-159 CIX ). TYPE HOST . — Mustelus schmitti Springer, 1939 (spiral valve) TYPE LOCALITY . — Coastal region of Mar del Plata ( 38º35’S , 57º33’W ), Province of Buenos Aires , Argentina . ETYMOLOGY. — The specific name schmittii refers to specific name of the host. LOCATION IN THE HOST. — Spiral valve. MATERIAL EXAMINED. — 10 specimens in toto (measurements based on 10 specimens ) ; two specimens in serial transverse sections. DESCRIPTION With the characters of the genus Orygmatobothrium as defined by Euzet (1994) . Body 17.49 (14.20-21.94) mm long by 250 (210-300) wide. Scolex 410 (350-500) in diameter possessing four circular bothridia with a muscular edge suspended by a very short peduncle. Bothridia 240 (220-290) in diameter; each bothridia with a central glandular organ ( 27-30 in diameter) and an accessory sucker 50 (45-70) in diameter. Two pairs of osmoregulatory ducts. Neck 620 (540-710) long and 100 (80-150) wide, provided with microtriches 6-8 long. Immature proglottids 20 (20-50) long by 80 (80- 100) wide; mature proglottids 480 (350-500) long by 290 (250-320) wide; gravid proglottids 5590 (4470-7250) long by 123 (100-148) wide. FIG. 1. — Orygmatobothrium schmittii n. sp. ; A , scolex; B , gravid proglottid (ventral view); C , cross section throught proglottid at level of ovary; D , detail of terminal genitalia with everted cirrus (lateral view); E , egg. Abbreviations: d , dorsal; v , ventral; o , ovary; od , oviduct; dod , dorsal osmorregulatory duct; vod , ventral osmoregulatory duct; mg , mehlis glands; va , vagin; vf , vitelline follicles; u , uterus. Scale bars: A-C, 0.2 mm; B, 1 mm; D, 0.05 mm; E, 0.01 mm. Segments with 193 (168-207) testes, subspherical 90 (60-120) long by 40 (60-80) wide. Testes are located in the medullary region, extending from the anterior part of the ovary to the anterior part of the proglottid. Vas deferens median, anterior and ventral; highly coiled before opening into cirrus sac. Cirrus sac thin-walled 480 (370-580) long by 150 (120-180) wide located ventrally in the lateral second third of the proglottid containg the ejaculatory duct and cirrus. Cirrus 220 (170- 250) long (partially invaginated) and 400-700 when fully protruded, with basal (proximal) bulbous shape, armed with microtriches about 10 long and a distal cylindrical end. Genital atrium ventro lateral and irregularly alternating 170- 300 in diameter. Ovary 940 (770-1140) in major diameter by 690 (560-790) in minor diameter located in posterior third of the proglottid, X shape in cross sections. Vagina opening anterior to cirrus sac in the genital atrium. Vaginal canal crossing the vas deferens ventrally, then, descending median and ventrally expanding into a seminal receptacle. Vagina, dorsal to the uterus. Oviduct receiving ducts of the seminal receptacle and median vitelline duct, continuing with the ootype surrounded by the Mehli’s glands. Uterus sac shape reaching the level of the cirrus sac opening to the exterior through the rupture of the ventral wall of the proglottid. Vitelline follicles extending from the posterior to the anterior part of the proglottid. Eggs 14-16 in diameter.