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 Nemertesia belini Bedot, 1916 ( Fig. 4 ; Table 1 ) Nemertesia belini Bedot, 1916: 1 ; 1917: 43 ; 1921a: 35 ; 1921b: 24 , Pl. IV figs 22–30; 1923: 215, fig. 1A–B; Rees & White, 1966: 280 ; Bouillon et al ., 1995: 59 . Not Nemertesia belini – Ansín Agís et al ., 2001: 200–204 , figs. 78–79, (= Nemertesia caboverdensis n. sp. ) Material examined. Nemertesia belini : Syntype material: Musée Océanographique , Monaco . Campagnes Scientifiques Prince Albert 1 er de Monaco : Expedition 1895, stn 584, 38°31´– 38°30´30”N , 26°49´15”– 26°50´15”W , 845 m , 16-VII-1895 : many colonies, several with damaged gonothecae. MOM 11 0139. Expedition 1897, stn 889, 37°57´30”N , 29°15´10”W , 208 m , 10-VIII-1897 : one damaged stem. MOM 11 0170. Expedition 1905, stn 2.210, 39°25´N , 31°22´30”W , 1229 m , 01-IX-1905 : one colony with hydrocladia alternately directed left and right in the basal part, no gonothecae. MOM 11 0199. Expedition 1903, stn without number, 32 miles ESE of Punta Este, Pico Island (Azores), 1160 m , 26-II-1903 : many colonies with gonothecae. MOM 11 0213. Biology. Bedot (1921b) indicated the presence of gonothecae in February and July. Distribution. Nemertesia belini was, to date, only known in the Azores. Its bathymetric range is between 208 and 1229 m ( Bedot 1916 , 1921b ). Description. Hydrorhiza tubular, adhering to substrate, giving rise to a monosiphonic and unbranched stem with several internal coenosarc canals. Axis divided into internodes separated by transverse nodes distinctly visible along the entire stem. Each internode with one to five apophyses distally and a variable number of nematothecae. Apophyses usually arranged in opposite pairs or verticils, in some cases also have been observed alternately directed left and right. There are a variable number of nematothecae between two consecutive apophyses. Length of apophyses varied in same colony, short basally and becoming longer distally. Basal apophyses with a small mamelon on the upper surface and four nematothecae: two axillar and two located distally to mamelon. Distal apophyses longer with a mamelon and may have up to 10 nematothecae: two axilar, two pairs above mamelon and between one and four unpaired distal nematothecae. Internal perisarc ring of varied development just under node separating the apophyses from hydrocladia. First hydrocladial internode in basal part of stem, short and ahydrothecate and provided with one or two nematothecae. Hydrocladia composed of succession of hydrothecate and ahydrothecate internodes, separated by slightly oblique nodes, but irregularly distributed, making it difficult to define a pattern for hydrocladial segmentation. Therefore, in the same colony, we have been observed hydrocladia with only hydrothecate internodes and other hydrocladia composed of hydrothecate and ahydrothecate internodes, which does not seem to be due to damage and subsequent regeneration. The regenerated part of a broken hydrocladia always shows regular heteronomous segmentation. Hydrothecate internodes with one hydrotheca and six or seven nematothecae: two or three mesial inferior, two laterals and two supracalycine nematothecae. Nevertheless, the number of nematothecae is variable between five and ten. Hydrothecae cup-shaped, adcauline wall fully adnate, abcauline wall straight and rim smooth and tilted upwards. In hydrocladia without ahydrothecate internodes, the hydrotheca is located in the middle of the internode, while in heteronomous hydrocladia it is placed in the basal half. Ahydrothecate internodes bearing one to three nematothecae, usually with two. All nematothecae bithalamic and movable. Likewise, in some hydrocladia after rupture and subsequent regeneration, three ahydrothecate internodes have been observed before the first hydrothecate internode. All internodes, hydrothecate and ahydrothecate, with two internal perisarcal rings of varied development, one in basal part and other in distal part. Gonothecae inserted on apophyses, near mamelon. Gonothecae curved, with one side clearly convex and other straight, with latero-terminal, ovoid-shaped aperture. Sex undetermined. Remarks. Bedot (1916) indicated that N. belini mainly differs from other Nemertesia species by considerable variability in the apophysis length, pattern of segmentation of the hydrocladia and number of unpaired nematothecae per hydrocladial internode (one to five mesial inferior and one or four supracalycine), making it difficult to establish diagnostic characters for the species. However, at the same time, this variability distinguishes N. belini from the other Nemertesia species. An exhaustive study of the variability in this species was published by Bedot (1921b) . This species is not represented in our collection; however, review of the type material was necessary to clearly identity some samples, and its redescription is included in this study. The differences between N. belini and N. freiwaldi n. sp. are discussed below.