A further step towards the characterisation of Terebellides (Annelida, Trichobranchidae) diversity in the Northeast Atlantic, with the description of a new species.

Several new species of genus Terebellides Sars, 1835 (Annelida, Trichobranchidae) have been recently described from the Northeast Atlantic Ocean after the detection of a large complex of species based on DNA sequence data from previous research. Some of those species (belonging to the so-called Group A) have already been described elsewhere. In this paper, we revise several Terebellides clades belonging to Groups B, C and D resulting in the identification of five nominal species: Terebellidesgracilis Malm, 1874, Terebellidesatlantis Williams, 1984, Terebellideswilliamsae Jirkov, 1989, Terebellidesirinae Gagaev, 2009, and Terebellidesshetlandica Parapar, Moreira & O'Reilly, 2016, plus one new species described here as Terebellideslavesquei sp. nov. All these species are characterised by a combination of morphological features complemented with a nucleotide diagnostic approach (specific COI nucleotides in the alignment position). Morphological characters used to discriminate between taxa refer to the branchial shape, presence/absence of ciliated papillae dorsal to thoracic notopodia and the morphology of thoracic and abdominal uncinal teeth. An updated identification key to all described species of this genus in NE Atlantic waters is also included.