Hydroids (Cnidaria, Hydrozoa) from Mauritanian Coral Mounds Author Gil, Marta Departamento de Ecoloxía e Bioloxía Animal, Facultade de Ciencias do Mar e Centro de Investigación Mariña (CIM-UVigo), Universidade de Vigo. Campus Lagoas-Marcosende. 36310 Vigo. Spain. & Instituto Español de Oceanografía, Centro Oceanográfico de Vigo. Subida Radio Faro 50. 36390 Vigo. Spain. Author Ramil, Fran Departamento de Ecoloxía e Bioloxía Animal, Facultade de Ciencias do Mar e Centro de Investigación Mariña (CIM-UVigo), Universidade de Vigo. Campus Lagoas-Marcosende. 36310 Vigo. Spain. & framil @ uvigo. es Author Agís, José Ansín Departamento de Ecoloxía e Bioloxía Animal, Facultade de Ciencias do Mar e Centro de Investigación Mariña (CIM-UVigo), Universidade de Vigo. Campus Lagoas-Marcosende. 36310 Vigo. Spain. & ansinjose @ gmail. com text Zootaxa 2020 2020-11-16 4878 3 412 466 journal article 7931 10.11646/zootaxa.4878.3.2 288c6fc9-269b-468f-8811-d79d4350f6e4 1175-5326 4425132 4F59F5B2-CFDB-4819-AF83-0EF232328F8D Lafoea gracillima ( Alder, 1856 ) Campanularia gracillima Alder, 1856: 361 , pl. 14, figs. 5, 6. Lafoea gracillima : Jäderholm, 1909: 74 , pl. 7, figs. 6, 7; Calder, 2012: 29–30 , fig. 28. Material examined. MAURIT-0911, stn MUDR01 , 16º08´24”N , 16º57´12”W , 488 m , 5-XII-2009 : two colonies, without coppiniae . MAURIT-0911, stn MUDR02 , 16º08´50”N , 16º57´01”W , 462 m , 5-XII-2009 : four colonies, no coppiniae . MAURIT-1011, stn MUDR20 , 16º08´11”N , 16º56´08”W , 405 m , 7-XII-2010 : two colonies, no coppiniae . MAURIT-1011, stn MUDR21 , 16º28´13”N , 16º51´43”W , 522 m , 9-XII-2010 : one colony 16 mm high, without coppiniae . MSM 16 /3, stn GeoB 14802–1, 20°14.791’N , 17°40.188’W , 595 m , 3-XI-2010 : two colonies, one colony with four isolated hydrothecae rising from stolon on coral, no coppiniae . MSM 16/3, stn GeoB 14886–1, 18°39.013’– 18°38.476’N , 16°43.580’– 16°43.757’W , 484–640 m , 12-XI-2010 : two colonies 10 mm high, one attached to Acesta excavata , and the other one to Madrepora oculata ; no coppiniae. Biology. This species has been found growing on shells and other hydroids ( Alder 1856 ) and on the stem of Tubularia indivisa Linnaeus, 1758 ( Calder 2012 ) . Jäderholm (1909) reported this species on rocky, shell and muddy bottoms in the Arctic Seas. The colonies studied by us were found growing on M. oculata , an unidentified coral and the bivalve A. excavata . Distribution. Lafoea gracillima is an Arctic and North Atlantic species distributed from Nantucket Sound in the west ( Calder 2012 ) to Mauritania in the east ( Gil & Ramil 2017a ). In West Africa, it was collected from Morocco [ Ramil & Vervoort 1992 ; Vervoort 2006 , both as Lafoea dumosa (Fleming, 1820) ], Canary Islands ( Vervoort 2006 , as L. dumosa ), Mauritania ( Gil & Ramil 2017a ) and Cape Verde Archipelago ( Vervoort 2006 , as L. dumosa ). The species was collected from depths of 20–30 m ( Calder 2012 ) to 365 m ( Jäderholm 1909 ). Many records of L. gracillima were included in L. dumosa or Lafoea fruticosa (Sars, 1851) , and, currently, it is not possible to provide an accurate overview of its actual distribution and habitat. Our material was collected from depths of 405 to 640 m . Remarks. Cornelius (1975) synonymised L. gracillima and L. fruticosa with L. dumosa , and his opinion was largely shared by later authors. In its current concept, L. dumosa is an almost cosmopolitan species with considerable variation in colony and hydrothecal morphology ( Vervoort 2006 ). Nevertheless, several authors have suggested the possibility of a species complex. Schuchert (2001) found differences in the measurements of the nematocysts of the stalkless L. dumosa and pedicellate L. fruticosa ; Moura et al. (2008) , using DNA barcoding, found two divergent genotypes within L. dumosa , suggesting the possibility of a cryptic species. Finally, Calder (2012) maintained L. gracillima as a valid species different from both L. dumosa and L. fruticosa . During the study of this collection, we compared this material with the typical stalkless L. dumosa collected from Galicia (Northwest Spain), and we are convinced that they are different species. Consequently, as per Calder (2012) we prefer to maintain L. gracillima as valid species.