Molecular Identity of Laonice cirrata (Sars, 1851) (Annelida, Spionidae) and Description of a New Laonice species from the Northwest Pacific

Abstract

Originally described from the northern Norway, Laonice cirrata (M. Sars, 1851) has been considered cosmopolitan and widely distributed in the North Pacific. To clarify the taxonomic status of the Pacific worms, we obtained the genetic characteristics of L. cirrata from Grøtsund Fjord, near Tromsø, one of the sites where Michael Sars collected worms to describe this species. The phylogenetic analysis of sequences of five gene fragments (mitochondrial COI and 16S rDNA, nuclear 18S rDNA and 28S rDNA, and Histone 3) showed significant difference between the Norwegian worms and worms from the north-western part of the Sea of Japan (Russia) earlier identified by morphology as L. cirrata. Common inhabitants of shallow waters in the Sea of Japan, these worms are assigned to the new species Laonice kasyanovi sp. nov. Both Northeast Atlantic and the Northwest Pacific populations exhibit high and overlapping variability of the diagnostic morphological characters of adults, and thus the two species can be considered as siblings. The distribution of these two species in the North Pacific remains uncertain and can only be elucidated by molecular data. Adults and one larva from the White Sea were also sequenced and found to be genetically identical to L. cirrata from Norway. The trochophores of L. cirrata are described and illustrated. They are characterized by two circles of large vesicles in the thick egg membrane and have been incorrectly referred to Aonides by previous authors.