To name but a few: descriptions of five new species of Terebellides (Annelida, Trichobranchidae) from the North East Atlantic Author Parapar, Julio Departamento de Bioloxia, Universidade da Coruna, Spain jparapar@udc.es Author Capa, Maria Departament de Biologia, Universitat de les Illes Balears, Spain Author Nygren, Arne Sjoefartmuseet Akvariet, Goeteborg, Sweden and Institutionen foer marina vetenskaper, Goeteborgs Universitet, Sweden Author Moreira, Juan Departamento de Biologia (Zoologia) & Centro de Investigacion en Biodiversidad y Cambio Global (CIBC-UAM), Facultad de Ciencias, Universidad Autonoma de Madrid, Spain https://orcid.org/0000-0002-1374-2033 text ZooKeys 2020 992 1 58 http://dx.doi.org/10.3897/zookeys.992.55977 journal article http://dx.doi.org/10.3897/zookeys.992.55977 1313-2970-992-1 0F038B5B120E45838E854092C9798566 6F09FA35C1585CCF8F9B519ADD7C0BFA Terebellides Group A (sensu Nygren et al. 2018) Description. The morphological features shared by all studied species in Group A are itemized below. Some of these are also shared by Groups B, C and D as defined in Nygren et al. (2018) (see Remarks below). Body appearance. Complete individuals ranging from 10.0-50.0 mm in length. Body tapering posteriorly with segments increasingly shorter and crowded towards pygidium (Fig. 14A-C ). Prostomium compact; large tentacular membrane surrounding mouth (Figs 5C , 14B ), with typical buccal tentacles with expanded tips (Figs 15A , 20A ). SGI as an expanded structure below tentacular membrane in a lower lip (Figs 14C , 15A , 22A , 24A ). Branchiae . Branchiae arising as single structure from SGIII, with a single stalked mid-dorsal stem (Figs 5A , 11C , 15A ), one pair of dorsal (upper) partially fused lobes (Figs 11B , 15B , 20A ), and a pair of shorter ventral (lower) lobes (Fig. 5A, B ) obscured or not by dorsal ones (Figs 5A, C , 15A, B ). Both dorsal and ventral branchial lobes ending each posteriorly in short terminal papilla (Fig. 20B ). Anterior projection of dorsal lobes (fifth lobe) present but short (Fig. 5A, B ) and usually obscured by tentacular membrane and buccal tentacles (Fig. 14A, C ). Posterior dorsal lobes reaching TC4 (Figs 3 , 4 , 19 ). Branchial lamellae provided with several parallel rows of cilia in inner face (Fig. 15C ); ciliated papillae not present, ciliary tufts present, sometimes not clearly visible (Fig. 5B, D ). Thorax . Eighteen pairs of notopodia (SGIII-SGXX) (Fig. 14B, D ), those of TC1 approximately as long as following ones (Figs 20A , 22A ) or slightly shorter (Fig. 15A ). Lateral lappets and dorsal projections of notopodia in anterior thoracic chaetigers with different degree of development depending on size and preservation conditions, but both more conspicuous on TC2-4/5 (Figs 15A , 22A ). All notochaetae as simple capillaries (Figs 11F , 15A ). Neuropodia as sessile pinnules from TC5 or TC6 to body end, with uncini in single or double rows, from TC7 throughout. Neuropodia on TC5 or TC5 and TC6, provided with several sharply bent, acute-tipped, geniculate chaetae (Figs 16B , 23A ) with minute teeth forming an ill-defined capitium only visible with SEM (Figs 12B , 25B ). From TC7, neuropodia with one or several rows of uncini per torus (Figs 16C , 23C ), with long shafted denticulate hooks, with large main fang (rostrum) longer than upper crest of teeth (capitium), which is composed by several teeth above main fang of decreasing length (Figs 23D , 25D, E ). Abdomen and pygidium . Approximately half as long as thorax and progressively thinner (Fig. 14B ). Neuropodia ranging from 18-38 chaetigers and forming erect pinnules (Figs 6F , 12F ) with several uncini per torus, number depending of specimen size. Uncini provided with several teeth above rostrum surmounted by a capitium composed of several teeth of decreasing length (Figs 6G , 16E , 21F ). Pygidium blunt, as funnel-like depression. Colour pattern . Colour in preserved specimens pale brown (Fig. 3 ). MG staining pattern 1 sensu Schueller and Hutchings (2010 : 10, fig. 4) and characterised by compact green colouration in CH1-3, then turning into striped pattern in CH4-12 and fading in following segments. Figure 3. STM photographs of several Terebellides species. A Terebellides bakkeni sp. nov. (species 10; holotype, ZMBN116395) B Terebellides stroemii Sars, 1835 (species 11; non-type specimen, ZMBN116397) C Terebellides kongsrudi sp. nov. (species 13; holotype, GNM14632) D Terebellides bigeniculatus Parapar, Moreira & Helgason, 2011 (species 20 + 28; non-type specimen, ZMBN116514) E Terebellides europaea Lavesque, Hutchings, Daffe, Nygren & Londono-Mesa , 2019 (species 6; non-type specimen, GNM14628) F Terebellides ronningae sp. nov. (species 7; holotype, ZMBN116357) G Terebellides norvegica sp. nov. (species 8; holotype, ZMBN416378) H Terebellides scotica sp. nov. (species 9; holotype, ZMBN116385). Abbreviations: bdl - branchial dorsal lobe; bvl - branchial ventral lobe; TC - thoracic chaetiger. Remarks. Among the aforementioned characters, branchial features might serve to distinguish most of Group A species (except for A3 species) from those in Groups B-D. Those include branchial size, lobes size (i.e., whether dorsal and ventral are of similar size or differ), presence of terminal papilla/filament on posterior lobes, and presence of ciliary structures (rows, tufts or buttons) on lamellae. Other taxa described or reported worldwide bear similar branchiae including T. stroemii sensu Parapar et al. (2011) from Iceland and sensu Parapar et al. (2013) from the Adriatic Sea, T. kerguelensis McIntosh, 1885 and T. longicaudatus Hessle, 1917 from Antarctic latitudes ( Parapar and Moreira 2008a , 2008b ), and T. kobei Hessle, 1917 from Japan ( Imajima and Williams 1985 ). Figure 4. Line drawings of several Terebellides species. A Terebellides bakkeni sp. nov. (species 10; holotype, ZMBN116395), anterior end, right lateral view B Terebellides stroemii Sars, 1835 (species 11; non-type specimen, ZMBN116397), anterior end, right lateral view C Terebellides kongsrudi sp. nov. (species 13; holotype, GNM14632), anterior end, left lateral view D Terebellides bigeniculatus Parapar, Moreira & Helgason, 2011 (species 20 + 28; non-type specimen, ZMBN116514), anterior end, left lateral view. Abbreviations: bdl - branchial dorsal lobe; bvl - branchial ventral lobes; dpn - dorsal projection of notopodium; TC - thoracic chaetiger. The other species groups as found in Nygren et al. (2018) were not studied in depth here and will be the aim of a subsequent study. However, Group B seems to be characterised by having a shorter body and free branchial lobes; these features are shared with T. atlantis Williams, 1984 and T. irinae Gagaev, 2009 as already suggested by Nygren et al. (2018) . Members of Group C are apparently not defined by any unique shared morphological character but show the same geographic distribution as T. irinae . Finally, the three putative species in Group D were related to T. gracilis Malm, 1874 and T. williamsae Jirkov, 1989 by Nygren et al. (2018) even though the latter was proposed to be synonymised with the former by Parapar et al. (2011) . These species seem characterised by having ventral white colouration in a number of anterior chaetigers and similar-sized branchial lobes; these characters are not shared with Group A. Figure 5. Terebellides bakkeni sp. nov. (species 10; paratypes, NTNU-VM-61376 and NTNU-VM-61377), SEM micrographs. A anterior end, left lateral view B, C branchial lamellae D branchial ciliary rows (framed in B ) E nephridial papilla F thoracic notopodial papillae (framed: detail of one papilla). Abbreviations: abl - anterior branchial lobe; bdl - branchial dorsal lobe; bvl - branchial ventral lobe; cr - ciliary row; ct - ciliary tuft; dpn - dorsal projection of notopodium; np - nephridial papilla; TC - thoracic chaetiger; tdp - thoracic dorsal papilla; tll - thoracic lateral lobes; tm - tentacular membrane. Regarding Group A, six morphological characters have been considered to delineate subgroups and species (Table 1 ). Two characters can be determined with the aid of the STM: 1) general branchial shape, 2) number of thoracic chaetigers with geniculate chaetae; four characters require SEM examination: 3) presence of papillae on lamellae of dorsal branchial lobes, 4) presence of ciliated papillae dorsal to thoracic notopodia, 5) features of thoracic and 6) abdominal uncini shape dentition. Branchial typology (1) is defined according to Parapar et al. (2016c) and thoracic uncini (5) follows Parapar et al. (2020) . Typology of abdominal uncini (6) is described here (see Discussion). Figure 6. Terebellides bakkeni sp. nov. (species 10; paratypes, NTNU-VM-61376 and NTNU-VM-61377), SEM micrographs. A TC6 (TU1) geniculate chaetae B geniculate chaeta (arrow pointing to capitium) C-E thoracic uncini F abdominal unciniger G detail of three abdominal uncini, frontal view. Furthermore, species will be also characterised according to geographic and bathymetric distribution according to available data.