Filellum bouvetensis Marques, Peña, Miranda & Migotto, 2011, sp. nov.

Filellum bouvetensis sp. nov.

(Figure 2 A–D)

Filellum contortum: Peña Cantero and Gili 2006: 766.

Non Lafoea contorta Nutting, 1905: 945, pl. 3, fig. 6, pl. 9, figs. 8–9 [= Filellum contortum (Nutting, 1905)].

Type series. Holotype— Filellum contortum (Nutting, 1905) (PS65/028), with coppiniae.

Type locality. From the holotype, 54o22.49’– 54o22.54’S; 0 3o17.58’– 03o17.21’E, 122–134m (Peña Cantero & Gili 2006: 765, 766).

Material examined. ANTARCTIC OCEAN: Bouvet Island, PS65/28 (25 November 2003, 122– 134m), colonies epibiotic on various hydroids (Antarctoscyphus elongatus, Schizotricha multifurcata, Sertularella sanmatiasensis, Symplectoscyphus sp.); with coppinia.

Description. Colonies stolonal, with filiform creeping hydrorhiza. Hydrotheca sessile, arising uprightly and almost completely free from hydrorhiza. When present, abcauline side of adnate part provided with a few striae. Hydrothecal aperture circular and slightly everted, usually with very long rim renovations. Free adcauline hydrothecal part 0.65– 0.187 mm long. Hydrothecal aperture 0.18–0.25 mm wide. Coppiniae up to 4 mm wide and 2 mm high, some almost completely surrounding the stem of the host hydroid, forming a ring of ca. 4 mm wide. Coppinia composed of firmly adpressed gonothecae with long defensive tubes at periphery, arching over the centre of the gonothecal mass and forming a corbula-like structure. Defensive tubes unforked and with distal aperture. Gonothecae elongated, roughly polygonal in apical view, but with a rather inconstant arrangement in lateral view; distal most part of gonothecae usually free and with irregular shape. Gonothecal aperture circular, situated on a very short, frequently unconspicuous, non-everted distal neck, 0.55–0.6 mm high, 0.1–0.2 mm wide and aperture 0.55– 0.6 mm wide. Cnidome composed of microbasic mastigophores (not seen discharged), 6.5–8.5 X3 –3.5 µm.

Distribution. Known only from Bouvet Island (Peña Cantero & Gili 2006).

Remarks. The material from Bouvet Island, here described as Filellum bouvetensis sp. nov., was identified as Filellum contortum (Nutting, 1905) by Peña Cantero and Gili (2006). Filellum bouvetensis sp. nov. is similar to Nutting’s (1905) species in the shape and size of the hydrothecae having a very long free hydrothecal part. However, the new species has larger nematocysts than those found in the lectotype of F. c o nt o r tu m. Furthermore, as indicated above, Nutting’s species was deprived of coppinia, rendering it an insufficiently characterized species to properly assign new material to. Therefore we have decided to consider the abundant, fertile, well-preserved and characterized material from Bouvet suitable for the creation of a new species.

Filellum bouvetensis sp. nov. is similar to F. a n t a rc t i c u m in the general shape of the coppinia, both with defensive tubes arching over the gonothecal mass, so that they form a sort of a corbula. Moreover, in dorsal view, the gonothecal aperture of F. bouvetensis sp. nov. is similar to that of F. a n t a rc t i c u m by the presence of a perisarc ring. However, in Hartlaub’s species the gonothecae lack any sort of neck and are distally homogeneous, being completely laterally adpressed. Both species also differ in the size and general proportions of the hydrothecae.

Filellum bouvetensis sp. nov. also resembles F. conopeum Watson, 2003 in the structure of the coppinia with defensive tubes curving over the gonothecae. However, Watson (2003) described the coppinia as bud-shaped, ca. 1 mm wide and 1 mm high, whereas in F. bouvetensis they are corbula-shaped and up to 4 mm wide and 2 mm high. Anyway, both species are clearly distinguishable by the size and relative proportions of the hydrothecae.

Here a new name is proposed for the Bouvet specimens, which can be clearly distinguished from the remaining known species of Filellum by the size of the nematocysts and hydrothecae, the structure of the coppinia and the shape and size of the gonothecae.

Etymology. The name bouvetensis refers to Bouvet, the name of the remote Southern Ocean island where this species was found.