Filellum antarcticum ( Hartlaub, 1904 )

Marques, Antonio C., Peña, Álvaro L., Miranda, Thaís P. & Migotto, Alvaro E., 2011, Revision of the genus Filellum Hincks, 1868 (Lafoeidae, Leptothecata, Hydrozoa), Zootaxa 3129, pp. 1-28 : 8-9

Filellum antarcticum ( Hartlaub, 1904)

Lafoea antarctica Hartlaub, 1904: 11 , pl. 2, fig. 2; Vanhöffen 1910: 311 –312, figs. 31a–c.

Reticularia antarctica: Totton 1930: 160 –161, fig. 17.

Filellum antarcticum: Millard 1964: 10 ; 1975: 177, figs. 58g –h; 1978: 171, 172, 192; Peña Cantero et al. 1998: 300; 2004b: 2283–2287, figs. 2c–f, 3, 4; Vervoort and Watson 2003: 57 –58; Peña Cantero 2008: 453; 2010: 764–765, figs. 3a–c.

Type series. The type specimen of Filellum antarcticum is lost ( Peña Cantero et al. 2004b: 2285). Neotype— Lafoea antarctica Vanhöffen, 1910 ; specimens on Symplectocyphus sp. ( ZMB Cni 14222) ( Peña Cantero et al. 2004b: 2285– 2286).

Type locality. From the original description of Lafoea antarctica Hartlaub, 1904 , it would be “S. Y. Belgica ” Expedition, Antarctic, Schwabber VII (70°23’S; 82°47’W, ca. 500 m, 8 October 1898), specimens on bryozoan ( Hartlaub 1904: 5). From neotype designation it is “Deutschen Southpolar Expedition”, Gauss Station, 65°21’S; 86°06’E, 385 m ( Peña Cantero et al. 2004b: 2285).

Material studied. ANTARCTIC: German Polarstern expedition–ANT II-4 Stn 310, Ronne Ice Shelf, Weddell Sea (76°52.0’S; 50°40.4’W, 252 m, 20 January 1984), “on Billardia subrufa , with coppinia” (RMNH-Coel. 30782); ANT II-4 Stn 341, Ronne Ice Shelf, Weddell Sea (76°39.2’S; 52°09.0’W, 297 m, 26 January 1984), “on B. subrufa and Stegella lobata , with coppinia” (RMNH-Coel. 30783); ANT II-4 Stn 438, Larsen Ice Shelf, Antarctic Peninsula, Weddell Sea (67°09.7’S; 54°21.4’W, 423 m, 7 February 1984), “on B. subrufa , with coppinia” (RMNH- Coel. 30785); ANT II-4 Stn 474, Ronne Ice Shelf, Weddell Sea (76°56.7’S; 49°44.0’W, 220 m, 14 February 1984), “on B. subrufa , with coppinia” (RMNH-Coel. 30788);?ANT II-4 Stn 524, Cape Norvegia, Princess Martha Coast, Weddell Sea (71°23.9’S; 13°58.8’W, 325 m, 25 February 1984), “on Halecium sp., with coppinia” (RMNH-Coel. 30790); ANT VIII-5 Stn 16-399, Riiser-Larsen Ice Shelf, Princess Martha Coast, Weddell Sea (72.86°S; 19.30°W, 380–390 m, 30 December 1989), “Bottom: large rocks”, “on B. subrufa , with coppinia” (RMNHCoel. 30794); ANT VIII-5 Stn 16-405, Ronne Ice Shelf, Weddell Sea, (76.52°S; 52.63°W, 330 m, 7 January 1990), “Bottom: mud”, “on B. subrufa ,? Opercularella belgicae , and axis of gorgonian, with coppinia” (RMNH-Coel. 30796); ANT VIII-5 Stn 16-456, Cape Norvegia, Princess Martha Coast, Weddell Sea (71.25°S; 12.01°W, 200 m, 26 January 1990), “on B. subrufa , with coppinia” (RMNH-Coel. 30816); ANT VIII-5 Stn 16-459, Cape Norvegia, Princess Martha Coast, Weddell Sea (70.96°S; 11.19°W, 350–380 m, 28 January 1990), “on B. subrufa , with coppinia” (RMNH-Coel. 30799); ANT VIII-5 Stn 16-486, Ronne Ice Shelf, Weddell Sea (76.50°S; 52.15°W, 330–340 m, 17 February 1990), “on B. subrufa , with coppinia” (RMNH-Coel. 30803); ANT IX-3 Stn 135, McDonald Ice Rumples, Caird Coast, Weddell Sea (75°27.9’S; 26°45.4’W, 221 m, 4 February 1991), “on B. subrufa , with coppinia” (RMNH-Coel. 30805). Deutsche Südpolar Expedition–Gauss Station (65°21’S; 86°06’E, 385 m), Museum für Naturkunde der Humboldt-Universität zu Berlin (neotype, ZMB Cni 14222) ( Peña Cantero et al., 2004b: 2284– 2285). Spanish Bentart 95 Expedition–Stn 3A, south of Livingston Island (62°37.7018’S; 60°22.8167'W, 92 m, 17 January 1995), on polychaete tube, with coppinia. Spanish Bentart 2003 Expedition–Stn 5A, south of Peter I Island (68°56’37’’– 68°56’43’’S; 90°35’50’’– 90°35’19’’W, 124 m, 4 February 2003), on Stegella lobata and the ascidian Cnemidocarpa verrucosa , with coppinia.

Description of neotype. (Complementing the description by Peña Cantero et al. 2004b: 2285): Colony stolonal, growing on monosiphonic stems of Symplectoscyphus sp., stolons creeping on substratum, hydrorhiza ca. 0.72–0.80 mm wide. Hydrothecae sessile, sock-shaped, arising with no definite pattern from hydrorhiza, varying in form, from about half of hydrotheca adnate to substratum to some completely free. Hydrothecae irregularly curved in diverse patterns, emerging from substrate plane at various angles. Adnate portion of hydrothecae tubular or maximally slightly flattened, 0.24–0.35 mm long, with numerous external transverse ridges on exposed side; free part cylindrical, smooth, 0.30–0.35 mm long; total adcauline wall 0.59–0.65 mm long, abcauline wall 0.55–0.63 mm long; hydrothecae slightly widening distally, margin even and smooth, with up to four renovations, slightly flaring; hydrothecal aperture circular, 0.104–0.130 mm wide. Hydranths not seen.

Gonothecae arranged in coppinia, ca. 2.4 mm wide. Gonothecae closely set, juxtaposed, their limits almost distinct in dorsal view, general shape tubular. Gonothecae 0.48 mm high, 0.11 mm wide, distally truncated with unraised circular aperture, 0.055 mm wide, rim even, not flared, without renovations. Protective tubes present, long, hollow, either forked or unforked, with distal circular aperture. Protective tubes usually curved towards center of gonothecal mass and merged to each other over gonothecae, forming a nest or corbula acting as an incubatory chamber. In one case, disk-shaped coppinia with defensive tubes forming two fused and disk-shaped structures, protecting gonothecae and eggs; in another case, coppinia as a semicircular structure. Eggs remaining inside gonothecae, immersed in a tissue mass presumed to be nourishing. Cnidome composed of two types of nematocysts, small (5.5– 6.5 X 2.6 µm) and large ones (10.4–12.4 X 4.2–5.2 µm).

Distribution. Filellum antarcticum seems to be “a shelf species” ( Peña Cantero et al. 1998: 300), being recorded from 13.5 m ( Millard 1964, 1975) to 423 m ( Peña Cantero et al. 2004b). The species has always been recorded epibiotic, on hydroids ( Vanhöffen 1910; Totton 1930; Peña Cantero et al. 2004b; Peña Cantero 2010), gorgonians ( Peña Cantero et al. 2004b), bryozoans ( Vanhöffen 1910; Millard 1964, 1975), cidarid spines ( Vanhöffen 1910), polychaete tubes ( Peña Cantero 2008), and ascidians ( Peña Cantero 2010). Coppinia found in austral summer ( Peña Cantero et al. 2004b: 2297). It is known from South Africa ( Millard 1964, 1975) and Antarctica , in the Davis Sea ( Vanhöffen 1910), Ross Sea ( Totton 1930), Weddell Sea ( Peña Cantero et al. 2004b), the South Shetland Islands ( Peña Cantero 2008), and off Peter I Island, in the Bellingshausen Sea ( Peña Cantero 2010).

Remarks. Filellum antarcticum was originally described as Lafoea antarctica by Hartlaub (1904) who, according to Peña Cantero et al. (1998: 300), diagnosed it as “sessile hydrothecae, with a short portion adnate to the substratum, followed by a long part directed upwards (this part being longer than in Filellum serpens ), and by the presence of numerous renovations of the hydrothecal rim”. However, these features are not sufficient to characterize a species of the genus.

The first solution in adequately describing Filellum antarcticum would be to study the type specimen. However, the type material of Lafoea antarctica Hartlaub, 1904 is reportedly lost ( Peña Cantero et al. 2004b: 2285). Therefore, Peña Cantero et al. (2004b) proposed the material described by Vanhöffen (1910) as the neotype of the species, since this specimen was the basis for the first description of the coppinia. Vanhöffen’s (1910) material was diagnosed by Peña Cantero et al. (2004b: 2286) as having “several coppiniae […] of varied shape […] all have in common a set of gonothecae surrounded by a fence of forked or unforked, defensive tubes provided with a distal circular aperture”. Peña Cantero et al. (2004b: 2286) emphasize that “this variability seems related to the nature of the substratum where the colony was growing” and when “there is enough surface for attachment of the stolonal tubes […] the coppinia is like a nest with the gonothecae surrounded by a fence of defensive tubes which arch over the gonothecae, whereas when there is not so much space, […] the coppinia has a disk or semicircular shape”. This plasticity is corroborated by several authors ( Totton 1930: 160; Millard 1975: 177) and calls attention to the difficulty in identifying boundaries of species in the genus Filellum .

Concerning the trophosome, as many other species congeners (viz. F. magnificum , F. nitidum , F. serratum ), F. antarcticum has striations on the outer part of the adnate wall and, therefore, the morphology of the coppinia is essential for the identification of the species. Filellum antarcticum has characteristic coppiniae with tubular gonothecae without distal neck and with bent protective tubes at the periphery of the coppinia, forming a structure that calls to mind a corbula. Differently, the gonothecae of F. magnificum are provided with a distal neck and the protective tubes may be either at the periphery or arise amongst gonothecae in the central area of the coppinia. Also, in F. nitidum , the coppinia has the surface covered by a thin, perforated, tissue layer; in addition, the hydrothecae of F. nitidum are spread on the coppinia together with the thin inverted, occasionally bifid, protective tubes. Finally, Peña Cantero et al. (2004b: 2286–2287) remarked that the differences between F. antarcticum and F. serratum are as follows: “the distally closed defensive tubes arise from amongst the gonothecae and curve over them forming a protective structure like a canopy” in F. serratum , whilst “the gonothecae are surrounded by a fence of distally open defensive tubes usually bent towards the centre of the gonothecal mass, constituting a nest or corbula” in F. antarcticum . Additionally, the gonothecae of F. serratum are “bottle-shaped, provided with a short and everted distal neck bearing the aperture, and are slightly shorter and wider”. The similarities in the trophosome of F. antarcticum and F. serratum led Peña Cantero et al. (2004b) to disregard the previous records of Filellum antarcticum not based on fertile specimens.