Abstract
The new tegastid species Smacigastes methanophilus sp. nov. is described from cold-seep samples collected from the Gulf of Mexico in 2006. Besides Smacigastes micheli Ivanenko & Defaye, 2004 and Smacigastes barti Gollner, Ivanenko & Martínez Arbizu, 2008, this is the third species of the genus Smacigastes Ivanenko & Defaye, 2004. To date, this genus contains the only species within the family Tegastidae known from deep-sea habitats. Furthermore, S. methanophilus sp. nov. is the first species of Tegastidae found at cold seeps and associated with tubeworm aggregations. It has the same primitive features as S. micheli but can be distinguished from the latter by the setation of second and third segments of female antennule and second segment of male antennule, the setation of the mandibular palp, the ornamentation of P5 exopod in both sexes, setation of male P5 exopod, form of the female P5 baseoendopod, and the different shape and length of the P5 setae in female. Moreover, both sexes of Smacigastes methanophilus sp. nov. are much smaller than those of S. micheli. Compared to S. barti, S. methanophilus sp. nov. differs in the segmentation and setation of female antennule, the setation of male antennule, setation of mandibular palp, setation of the maxillule, number of endites of the maxilla, number of setae in P1, the ornamentation of female P5 and setation in male P5.References
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