Straightening the striped chaos: Systematics and evolution of Trypanosyllis and the case of its pseudocryptic type species Trypanosyllis krohnii (Annelida, Syllidae)

Abstract

All members of the syllid genus Trypanosyllis show distinctive flattened, ribbon-like bodies and a pharynx armed with a trepan; however, the phylogenetic relationships within this genus remain unsettled, especially with respect to the genera Eurysyllis and Xenosyllis (morphologically similar). To resolve this systematic uncertainty we analysed the phylogenetic relationships of a worldwide sampling of specimens of Trypanosyllis and three related genera using multiple molecular markers. We show that Trypanosyllis as presently construed is paraphyletic, and identify a clade of striped species that were previously all considered to be Trypanosyllis zebra (Grube, 1860). We outline the case to consider Trypanosyllis krohnii Claparede, 1864 as the type species of the genus, instead of Trypanosyllis zebra. Trypanosyllis krohnii (interpreted as Trypanosyllis zebra by recent authors) was previously believed to be cosmopolitan, but we show that it includes at least seven cryptic and pseudocryptic species, five of which are described herein: Trypanosyllis kalkin sp. nov., Trypanosyllis californiensis sp. nov., Trypanosyllis luquei sp. nov., Trypanosyllis leivai sp. nov., and Trypanosyllis taboadai sp. nov. In addition, Trypanedenta gemmipara (Johnson, 1901) comb. nov. and Trypanedenta gigantea (McIntosh, 1885) comb. nov., previously included in Trypanosyllis, are here transferred to Trypanedenta Imajima & Hartman, 1964, and Pseudosyllis brevipennis Grube, 1863 [previously named Trypanosyllis coeliaca (Claparede, 1868)] is transferred to the resurrected genus Pseudosyllis Grube, 1863. Overall our results show a complex scenario of speciation, with cases of pseudocryptic species that correspond to geographically restricted lineages.