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Phylogenetic relationships and evolution of reproductive modes within flattened syllids (Annelida, Syllidae) with the description of a new genus and six new species
Syllids annelids from the so-called ‘ribbon clade’ are flattened, ribbon-shaped worms of the genera Parahaplosyllis, Eurysyllis, Xenosyllis, Trypanosyllis, Ramisyllis, Trypanobia, Plakosyllis, Pseudosyllis, and Trypanedenta. Some species possess a remarkable reproductive strategy using multiple stolons that has been recently suggested to be ancestral to the group. Here, in order to evaluate the evolution of reproductive modes in the group, we assess for the first time, the phylogenetic relationships within the so-called ‘ribbon clade’ and related genera. We collected new material of Trypanobia and Trypanosyllis from Japan, Spain, Philippines, and Indonesia and sequenced it for the nuclear markers 18S rRNA and the mitochondrial markers 16S rRNA and cytochrome c oxidase I for phylogenetic inference and also performed ancestral character reconstruction for the reproductive strategy in the entire group. The formal taxonomical descriptions of a new genus and six new species of Trypanosyllis are provided. Most genera within the ‘ribbon clade’ are monophyletic and the relationships appeared well supported in most cases. However, our phylogenetic hypotheses are not conclusive in regard to the relationships of the genera Trypanedenta and Trypanobia, or to their status as distinctive genera, since they seem to be paraphyletic and they appear in low-supported clades. In contrast, our results shed light into the evolution of the reproductive modes within Syllinae, showing that scissiparity (development of a single stolon each time) is the ancestral character for the entire group and gemmiparity (development of more than one stolon at the same time) then appeared twice in two independent clades.
IS17011 Accepted 09 July 2017
© CSIRO 2017