A further step towards the characterisation of Terebellides (Annelida, Trichobranchidae) diversity in the Northeast Atlantic, with the description of a new species Author Barroso, Maria https://orcid.org/0000-0001-9624-3602 Departamento de Bioloxia, Universidade da Coruna, A Coruna, Spain maria.p.barroso@udc.es Author Moreira, Juan https://orcid.org/0000-0002-1374-2033 Departamento de Biologia (Zoologia) & Centro de Investigacion en Biodiversidad y Cambio Global (CIBC-UAM), Facultad de Ciencias, Universidad Autonoma de Madrid, Madrid, Spain Author Capa, Maria https://orcid.org/0000-0002-5063-7961 Departament de Biologia, Universitat de les Illes Balears, Mallorca, Spain Author Nygren, Arne https://orcid.org/0000-0001-5761-8803 Sjoefartmuseet Akvariet, Goeteborg, Sweden & Institutionen foer marina vetenskaper, Goeteborgs Universitet, Goeteborg, Sweden Author Parapar, Julio https://orcid.org/0000-0001-7585-6995 Departamento de Bioloxia, Universidade da Coruna, A Coruna, Spain text ZooKeys 2022 2022-11-28 1132 85 126 http://dx.doi.org/10.3897/zookeys.1132.91244 journal article http://dx.doi.org/10.3897/zookeys.1132.91244 1313-2970-1132-85 4168C32E37A74912A9094912E69030AA E57A2873FAAC552282A3E1390FF28D3E Terebellides irinae Gagaev, 2009 Figs 3D , 4C , 9 , 10D , 11 , 12 , 13 Terebellides irinae Gagaev, 2009: 474-478. Terebellides irinae Species 24 - Nygren et al. 2018 : 18-22, figs 6, 10. Material examined. 6 specimens (Suppl. material 1), Arctic Ocean (ZMBN116496, ZMBN116497, ZMBN116498, ZMBN116499, ZMBN116500, ZMBN116501). GenBank accession numbers of material examined (COI). MG025340, MG025341, MG025342, MG025343, MG025344 . Diagnostic features of studied material. Incomplete individuals ranging from 10.0-17.0 mm in length (Fig. 9 ). Branchial dorsal lobes provided with filaments, 75.0 µm in length (Fig. 3D ) and branchial ventral lobes reduced, distinctly smaller than dorsal ones (Fig. 4C ). Dorsal lobes provided with seven lamellae (Fig. 4C ). Lateral lappets present on TC 1-4; dorsal projection of thoracic notopodia on TC 2-5 (Fig. 3D ). Geniculate chaetae in TC 5, acutely bent and provided with hardly distinguishable capitium (Fig. 13B ). Ciliated papilla dorsal to thoracic notopodia not observed. From TC 7, neuropodia with one row of type 3 thoracic uncini per torus, with rostrum/capitium length ratio of ~ 2:1 and capitium with a first row of four or five medium-sized teeth, followed by several smaller teeth (Fig. 13C, D ). Abdomen with at least 20 pairs of neuropodia with type 2 uncini (Fig. 13E, F ). Colour pattern. MG staining pattern characterised by compact green colourant in SG 1-4, then turning into striped pattern in SG 5-14 and fading in following segments (Fig. 12 ). Similar to pattern 1. Nucleotide diagnostic features. All sequences of Terebellides irinae share and are distinguished from other available Terebellides sequences in unique combinations of nucleotides (underlined) at the given position of our alignment: 177-204: CGGGGGGTTTGGAAACTGGTTAATCCCC, 213-225: TGGGGCCCCAGAC, 249-258: CATAAGGTTC, 273-303: GGCCCTCATCCTACTAGTCAGCTCAGCTGCT, 305-321: GGCTGGT, 327-336: ATGAACTGTA, 342-372: ACCACTTTCAGACAACATCGCTCATGCCGGA, 381-399: AGATCTAGCAATTTTCTCA, 426: CCTAGGTTCTATTAACTTCATCACAACAGTC, 483-499: TCTAGAACGAATCCCAC, 535-573: TTATTACTATCACTACCAGTGCTAGCCGGAGCTATTACC, 594-612: CATTAACACATCATTCTTC, 618-636: AGCCGGTGGTGGTGATCCT. Type locality. Arctic Ocean, 73°04'N , 157°12'W ( Gagaev 2009 ). Distribution and bathymetry. Arctic Ocean; 4038-4380 m deep (Figs 10D , 11 , Suppl. material 1). Remarks. Terebellides irinae is a small species, reaching up to 17 mm in length and is characterised by the lack of papillae on margins of branchial lamellae, and by having branchiae of type 4, filaments in ventral branchial lobes, thoracic uncini of type 3 and abdominal uncini of type 2 (Table 1 ). Jirkov and Leontovich (2013) proposed T. irinae as synonym of T. stroemii because it fit within the variability of the latter. However, Parapar and Hutchings (2014) redescribed T. stroemii designating a neotype and T. irinae not fit in this concept. Later, Nygren et al. (2018) recognised T. irinae as different from T. stroemii after molecular analyses and pointed out that T. irinae is the only species present in the Arctic Ocean at depths below 4000 m (Fig. 11 ). Furthermore, T. irinae is the only species in Northeast Atlantic Ocean bearing branchiae of type 4 and therefore is also considered as a valid species in this work. Other taxa from elsewhere such as T. mira and T. rigel also bear the same branchial type, these two species have branchial lobes free from each other with few numbers of not packed lamellae and ventral lobes are also distinctly smaller than the dorsal ones.