Filellum sp.

Gil, Marta & Ramil, Fran, 2021, Hydroids (Cnidaria, Hydrozoa) from the Vema and Valdivia seamounts (SE Atlantic), European Journal of Taxonomy 758, pp. 49-96 : 56

Filellum sp.

Fig. 2F ; Table 1

Material examined

SOUTH ATLANTIC OCEAN • 2 colonies (1 growing on an antipatharian, 1 on Sertularella patagonica ), no coppinia; Vema Seamount , stn PT4; 31°39′43″–31°38′10″ S, 8°22′37″–8°23′42″ E; 50–108 m depth; 31 Jan. 2015; SEAFO-2015 leg.; SEAFO-2015-40003 , SEAFO-2015-40033 • 4 colonies (3 growing on Campanularia hincksii , 1 on a bryozoan), no coppinia; Vema Seamount , stn Dive 3; 71–935 m depth; 31 Jan. 2015; SEAFO-2015 leg.; SEAFO-2015-40132 , SEAFO-2015-40257 , SEAFO-2015-40921 • 1 colony, growing on Amphisbetia distans , no coppinia; Vema Seamount , stn Dive 4; 91–95 m depth; 1 Feb. 2015; SEAFO-2015 leg.; SEAFO-2015-40661 .

Description

Stolonal colonies arising from a filiform hydrorhiza creeping on other hydroids and a bryozoan. Hydrorhizal stolons give rise to small, tubular hydrothecae adnate for ca half their length; adnate part parallel to hydrorhiza, upper, free part provided with numerous and very faint striations on abcaulinar side, and bent upwards from hydrorhiza at an angle between 45° and 90°, although only occasionally perpendicular to the adnate part; aperture circular, rim even, only slightly everted; renovations have not been observed. Cnidome: two size classes of nematocysts, with small (10–12.5× 5–7.5 µm) and large (15–17.5 × 7.5–10 µm).

Coppinia absent.

Remarks

The shape of the hydrothecae in the colonies studied herein resembles those of Filellum serratum (Clarke, 1879) , Filellum antarcticum (Hartlaub, 1904) and Filellum magnificum Peña Cantero, Svoboda & Vervoort, 2004 , due to the presence of numerous transversal striations of the adnate part. Nevertheless, the measurements of both hydrothecae and nematocysts do not match with those of the species mentioned above. In our material, the hydrothecae are smaller and the nematocysts larger than those of F. serratum , F. antarticum and F. magnificum . Based on these differences, we considered this material to be a different species, but the absence of coppinia prevents us from establishing a more accurate identification.

Figures

Fig. 2. A–E. Amphinema biscayana (Browne, 1907). A. Colony. B. Cross-section of the main stem. C. Part of branch with polyps. D. Part of branch with polyp and medusa bud. E. Part of main stem with polyp. — F. Filellum sp., several hydrothecae.