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چکیده
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In the present study two new species of Tetragonocephalum Shipley et Hornell, 1905, T. mackenziei sp. n. and T. kazemii sp. n., are described from the spiral intestine of the cowtail stingray, Pastinachus sephen (Forsskål), from the northern coast of the Gulf of Oman. Tetragonocephalum mackenziei is distinguished from the 16 other valid species of Tetragonocephalum by a unique combination of characteristics, i.e. sperm-filled seminal receptacle in immature proglottids, body length (7.7-17.5 mm), body width (213-288 µm), number of proglottids (34-49), number of testes (10-14), size of scolex (228-315 µm × 213-288 µm) and size of acetabula (56-73 µm × 61-75 µm). Tetragonocephalum kazemii is morphologically distinguishable from its valid congeners and T. mackenziei based on a combination of characteristics, including body length (28.8-36.6 mm), number of proglottids (50-65), number of testes (30-42), size of scolex (388-564 µm × 326-448 µm), size of acetabula (62-86 µm × 57-90 µm) and testes (25-39 × 21-32). This brings the total number of validly described species of Tetragonocephalum to 18 and expands our knowledge of this diverse genus to now include the Gulf of Oman, as well as Arafura Sea, northern Indian Ocean and western Pacific Ocean.
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