Polymastiidae (Porifera: Demospongiae) of the Nordic and Siberian Seas

We would like to express our gratitude to all colleagues, who kindly provided the access to the sponge collections of their institutions: Jean-Marc Gagnon (Canadian Museum of Nature, Ottawa), Erica Mejlon (Museum of Evolution, University of Uppsala), Kennet Lundin and Carola Azurduy Högström (Gothenburg Natural History Museum), Miche`le Bruni (Musée Océanographique de Monaco), Carsten Lüter (Museum für Naturkunde, Berlin), Isabelle Domart-Coulon (Muséum National d'Histoire Naturelle, Paris), Clare Valentine, Andrew Cabrinovic and Emma Sherlock (Natural History Museum, London), Nicole de Voogd and J. Koos van Egmond (Naturalis Biodiversity center, Leiden), Lutz Bachmann and Ase Ingvild Wilhelmsen (Natural History Museum, University of Oslo), Ole Secher Tendal (Natural History Museum of Denmark, University of Copenhagen), Bernard E. Picton (Ulster Museum, National Museums of Northern Ireland, Belfast), Jon Anders Kongsrud (University Museum of Bergen, Natural History Collections), Torkild Bakken (University Museum of the Norwegian University of Science and Technology, Trondheim), Olga Bozhenova (Zoological Institute of Russian Academy of Sciences, Saint-Petersburg). We are also thankful to Bjørn Gulliksen (University of Tromsø), Bjørn Tore Dragnes (OMNIMAR Dragnes, Tromsø), Peter Leopold (University Centre in Svalbard) and Erling Svensen (OceanPhoto/Dalane Tidende AS, Egersund), who arranged the sampling of fresh material along the Norwegian Coast and on Svalbard and provided us with high-quality underwater images. The colleagues, who granted us fresh samples from other regions, are also greatly acknowledged: Christine Morrow (Department of Zoology, Ryan Institute, National University of Ireland, Galway) and Bernard E. Picton (Ulster Museum, National Museums of Northern Ireland, Belfast) for the samples and photos of sponges from the British Isles, Javier Cristobo and Pilar Rios (Spanish Institute of Oceanography, Madrid) for the samples from Mozambique, and Natalia Chervyakova (Moscow State University) for the material from the White Sea. Paco Ca ́rdenas (BioMedical Centre, Uppsala) is acknowl- edged for the photos of sponges from Museum of Evolution, University of Uppsala. Thanks also come to Egil Severin Erichsen and Irene Heggstad (University of Bergen, Laboratory for Electron Microscopy) for their careful assist- ance at SEM, to Kenneth Meland, Solveig Thorkildsen and Louise Lindblom (University of Bergen, BioDiversity Laboratories at the Department of Biology) for their great assistance under the obtaining and treatment of molecular data and to Endre Willassen (University Museum of Bergen, Natural History Collections) and Oliver Voigt (Ludwig-Maximilians-Universität München, Palaeontology and Geobiology) for their inestimable help with the phylogen- etic computing. Last but not least, we would like to thank the two reviewers for the great work they have done when reading our manuscript. This study was supported by the Norwegian Biodiversity Information Centre, Artsdatabanken (project No. 70184219), the Norwegian Academy of Science and Letters (grant to HTR), the Research Council of Norway (through contract No. 179560) and the European Union's Horizon 2020 research and innovation programme under grant agreement No. 679849 (the SponGES project). The visit of AP to the Natural History Museum (London) in 2010 received funding from the SYNTHESYS Project (http://www. synthesys.info/) financed by European Community Research Infrastructure Action under the FP7 Integrating Activities Programme. COPYRIGHT: © Marine Biological Association of the United Kingdom 2017 This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.