Abstract

The original description of the genus Tetragonocephalum was published more than one hundred years ago but its taxonomic status was clarified only recently. To date, approximately 30 nominal species of this genus have been described, mostly from the northern Indian Ocean, but nearly half of them are invalid and only 14 species are recognized as valid. In the present study two new species of Tetragonocephalum are described from the spiral intestine of Himantura randalli from off Jod, on the northern coast of the Gulf of Oman. Tetragonocephalum sabae sp. n. is distinguishable from the valid species of Tetragonocephalum based on number of proglottids (43−53), number of testes (42−50), and size of scolex (401−453×328−455), acetabula (87−109×72−116), mature proglottids (802−1,333×226−336), cirrus sac (92−160×103−154), and eggs (16−19×11−13). Tetragonocephalum salarii sp. n. can be distinguished from Tetragonocephalum sabae sp. n. and all other valid species of Tetragonocephalum based on number of proglottids (77−86). Furthermore, it differs from its congeners based on a combination of some characteristics, including the number of mature (3−7) and gravid (18−20) proglottids, the number of testes (30−38), and the size of acetabula (84−111×80−96), mature proglottids (497−833×334−403), gravid proglottids (1,036−1,482×440−575), testes (20−34×31−50), ovary (123−215×210−278), and eggs (24−45×13−21).

Highlights

  • Shipley and Hornell (1905) erected Tetragonocephalum and described two new species, the type species T. trygonis Shipley & Hornell, 1905 from Himantura walga (Müller & Henle) and T. aetiobatidis Shipley & Hornell, 1905 from Aetobatus ocellatus (Kuhl), collected from fishes taken from the Gulf of Manaar off the coast of Ceylon ( Sri Lanka)

  • We describe two new species of this genus collected from the spiral intestine of the Arabian banded whipray, Himantura randalli Last, ManjajiMatsumoto & Moore, 2012

  • Tetragonocephalum salarii sp. n. can be distinguished from T. sabae sp. n. and all other valid species of Tetragonocephalum by the number of mature and gravid proglottids, the number of testes; and the size of acetabula, mature proglottids, gravid proglottids, testes, ovary, and eggs

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Summary

Introduction

Shipley and Hornell (1905) erected Tetragonocephalum and described two new species, the type species T. trygonis Shipley & Hornell, 1905 from Himantura walga (Müller & Henle) (as Trygon walga) and T. aetiobatidis Shipley & Hornell, 1905 from Aetobatus ocellatus (Kuhl) (as Aetiobatis [sic] narinari), collected from fishes taken from the Gulf of Manaar off the coast of Ceylon ( Sri Lanka). Since 2006, some new species of Tetragonocephalum have been proposed, i.e., T. govindi Khamkar & Shinde, 2012 (Khamkar and Shinde 2012); T. panjiensis Khamkar, 2011 (Khamkar 2011); T. pulensis Kankale, 2014 (Kankale 2014); T. ratnagiriensis Khamkar, 2012 (Khamkar 2012); T. sepheni Lanka, Hippargi & Patil, 2013 (Lanka et al 2013). These species do not follow the rules of ICZN, and especially violate Article 16, they are unavailable (ICZN 1999). The only study on Tetragonocephalum from the Gulf of Oman was conducted by Golestaninasab et al (2014) who showed that the genus Tetragonocephalum can act as a heavy metal bioindicator in the marine environment

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