Filellum serratum

Filellum cf. serratum (Clarke, 1879)

(Fig. 2 C–E)

Filellum serratum: Millard, 1975: 178, fig. 59A–C; Millard, 1978: 177; Hirohito, 1995: 110–112, fig. 31a–c; Calder, 1998: 1852–1853; Peña Cantero et al., 1998: 304–308, fig. 1–2; Marques et al., 2011.

Filellum cf serratum: Ramil & Vervoort, 1992: 54–55; Vervoort, 2006: 231–232.

Material examined. MAURIT-0911, stn MUDR 01, 16º08´24”N, 16º57´12”W, 488 m, 5-XII-2009: 26 colonies, 9 attached to bryozoans, five to Eudendrium sp. and one to Aglaophenia lophocarpa; no coppiniae.

MAURIT-0911, stn MUDR02, 16º08´50”N, 16º57´01”W, 462 m, 5-XII-2009: one colony on Sertularella gayi, without coppiniae.

MAURIT-0911, stn MUDR07, 18º35´40”N, 16º43´12”W, 460 m, 12-XII-2009: three colonies, on Turritopsis sp., without coppiniae.

MAURIT-1011, stn MUDR20, 16º08´11”N, 16º56´08”W, 405 m, 7-XII-2010: three colonies, growing on Lafoea gracillima and bryozoans, no coppiniae.

MSM 16/3, stn GeoB 14801–1, BG, 20°14.762’N, 17°40.173’W, 568 m, 3-XI-2010: six colonies, four on Aglaophenia lophocarpa and one on Nemertesia freiwaldi n. sp., no coppiniae.

MSM 16 /3, stn GeoB 14802–1, BG, 20°14.791’N, 17°40.188’W, 595 m, 3-XI-2010: one colony attached to coral, without coppiniae.

MSM 16 /3, stn GeoB 14886–1, ROV, 18°39.013’– 18°38.476’N, 16°43.580’– 16°43.757’W, 484–640 m, 12- XI-2010: one colony on Sertularella gayi, no coppinia.

MSM 16/3, stn GeoB 14908–1, ROV, 17°40.213’– 17°40.191’N, 16°40.829’– 16°40.289’W, 463–574 m, 16- XI-2010: nine colonies, three attached to Halecium sibogae marocanum, two to Sertularella gayi, two growing on bivalvia, two on unidentified hydroids, no coppiniae.

MSM 16 /3, stn GeoB 14911–1, CKG, 17°28.910’N, 16°41.509’W, 450 m, 16-XI-2010: two colonies, on a bryozoan, without coppiniae.

MSM 16 /3, stn GeoB 14914–1, ROV, 17°08.203’– 17°07.898’N, 16°49.478’– 16°48.878’W, 417–514 m, 17-XI- 2010: one colony growing on Sertularella gayi, without coppiniae.

Biology. Filellum serratum has been found growing on several substrata, mainly on hydroids but also on bryozoans, anthozoans, worm tubes and algae (Peña Cantero et al. 1998; Vervoort 2006). Fertile material has been found in March, July and August (Peña Cantero et al. 1998).

The colonies studied here were mainly growing on bryozoans and the hydroids A. lophocarpa Allman, 1877, N. freiwaldi n. sp., H. sibogae marocanum, S. gayi, Eudendrium sp., Turritopis sp. and L. gracillima. No coppiniae were found.

Distribution. It is a circumglobal species (Peña Cantero et al. 1998); however, most identifications are based on sterile material, and, in consequence, its actual distribution remains uncertain (Vervoort 2006). In West Africa, it was collected from Canary Islands (Vervoort 2006), Mauritania (Gil & Ramil 2017a) and Cape Verde Archipelago (Vervoort 2006). The bathymetric distribution ranges between 0 and 2000 m (Millard 1978; Calder 1998).

Our material was collected from depths of 405 to 640 m.

Description. Colonies stolonal, hydrorhizal stolons giving rise to tubular hydrothecae with the adnate part with fine transversal striae or corrugations on its upper surface; free part curving away from the adnate part, resulting in an erect distal part of variable length, varying between one-third to three-fourth of hydrothecal length. Hydrothecal rim circular, smooth and slightly everted. Renovations of hydrothecae are common and on occasion numerous, oscillating between one and eight. Coppinia not observed.

Remarks. Identification of the different species of Filellum requires the study of its coppiniae (Marques et al. 2011); however, all the material studied by us was sterile. The hydrothecae showed the characteristic transverse striae of F. serratum, the only species with the hydrothecal wall striated in the Atlantic; consequently, we identified it tentatively F. cf. serratum. Filellum antarcticum (Hartlaub, 1904), Filellum magnificum Peña Cantero, Svoboda & Vervoort, 2004 and Filellum nitidum Watson, 2005 also have striated hydrothecae, but they are only known in the Antarctic and South Africa, Antarctic and Australia, respectively. Nevertheless, some differences in coppinia morphology within the fertile material assigned to F. serratum by several authors suggest that several species could be involved in its current definition (see Peña Cantero et al. 1998 and Marques et al. 2011).