Halecium tenellum: Cornelius, 1975: 409–411, fig. 12; Ramil & Vervoort, 1992: 90–91, fig. 21f, g; Cornelius, 1995a: 296-297, fig. 69; Peña Cantero & García Carrascosa, 2002: 75–77, fig. 12c–e; Vervoort, 2006: 254.
Material examined. MAURIT-0911, stn MUDR01, 16º08´24”N, 16º57´12”W, 488 m, 5-XII-2009: one colony, attached to Lophelia pertusa, no gonothecae.
Biology. This species has been found growing frequently on other hydroids and on rocks, pebbles and as epibiont on algae and a wide range of invertebrates (Peña Cantero & García Carrascosa 2002). Fertile material has been found in January, April, May, June, October and December (Peña Cantero & García Carrascosa 2002; Medel & Vervoort 2000).
The colony studied by us was growing on L. pertusa.
Distribution.Halecium tenellum is a near cosmopolitan species (Cornelius 1975), with records in all oceans, including polar waters. Its distribution was reviewed in detail by Medel & Vervoort (2000), but some identifications from high latitudes in the North Atlantic are erroneous (Calder 1991; Schuchert 2005). In West Africa, it was collected from Morocco (Patriti 1970; Ramil & Vervoort 1992), Canary Islands (Vervoort 2006), Mauritania (Gil & Ramil 2017a), Cape Verde Islands (Medel & Vervoort 2000; Vervoort 2006), Guinea-Bissau (Vervoort 1959; Gili et al. 1989), Guinea (Vervoort 1959) and Ghana (Buchanan 1957; Vervoort 1959). Its bathymetric range extends from the intertidal zone to 1200 m (Peña Cantero & García Carrascosa 2002).
Our material was collected from a depth of 488 m.
Remarks. Although gonothecae were absent in our material, the delicate aspects of the colony, such as long, thin and straight internodes disposed in zigzag directions, well-developed primary hydranthophores and stark flared hydrothecal rim, allowed us identify it as H. tenellum.