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An athecate hydrozoan, Serehyba sanctisebastiani, representing a new genus, is described. It possesses gonosomes with a cormidium-like structure unique among tubulariids: a distal set of branched nematophores and a proximal gonodendron. S. sanctisebastiani is apparently transitional between the families Tubulariidae and Corymorphidae. It is a symbiont of the gorgonian octocoral Lophogorgia punicea (Milne Edwards & Haime, 1857).
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Silveira et al. (1984) studied this question.
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