Halecium interpolatum Ritchie 1907

Halecium interpolatum Ritchie, 1907

(Figs 5 G–J, 8A–B)

Halecium interpolatum Ritchie, 1907: 526, pl. 1 fig. 3, pl. 2 fig. 3; Rees & Thursfield, 1965: 107, 197; Smaldon, Heppell & Watt, 1976: 17; Stepanjants, 1979: 103, pl. 16 fig. 7; Blanco, 1994a: 156; 1994b: 186; Vervoort & Watson, 2003: 86; Watson, 2008: 171 –172, fig. 7A, B.

Halecium ovatum Totton, 1930: 143, fig. 3; Vervoort, 1972b: 339, fig. 1; Stepanjants, 1979: 103, pl. 20 fig. 1a–g; Blanco, 1994a: 156; 1994b: 187; Peña Cantero & García Carrascosa, 1995: 12 –13, fig. 2G–H; 1999: 212 et seq.; Vervoort & Watson, 2003: 86; Peña Cantero, 2004: 769; 2008: 455, fig. 1e–g; 2009: 1747, fig. 2f; 2013: 128, fig. 3e; Watson, 2008: 172 –173, fig. 8A, B; Peña Cantero & Vervoort, 2009: 85, fig. 1f; Galea & Schories, 2012b: 9, fig. 2J–K; Peña Cantero et al., 2013: 745–747, fig. 6b.

Halecium tenellum —Stepanjants, 1972: 72; Blanco, 1984: 10 –11, pl. 6 figs 14–15.

Halecium tubatum Watson, 2008: 174 –175, fig. 10A, B (in part).

? Halecium ovatum —Watson, 2003: 166, fig. 15D, E.

Material examined. Scottish National Antarctic Expedition 1902–1904: Scotia Bay, South Orkneys, 06–12–1903; RSM 1921.143.1328 Leptotype of H. interpolatum, several stems, up to 35 mm high [in addition, one microslide (1959.33.153) with one stem, c. 23 mm high]; RSM 1921.143.1328A, Paratype of H. interpolatum, several stems, up to 35 mm high. BANZARE [as H. tubatum by Watson (2008)], Stn 105, 67°46'S 67°03'E (Mawson Coast), 13–02– 1931, 163 m; two microslides (Hydr. 710/12): F147470.2, a few incipient stems in bad condition, and F147470.3, hydrorhiza with just two incipient stems. Spanish Antarctic Expedition Bentart 95 [H. ovatum by Peña Cantero (2008)]: Stn 27A, several stems, up to 35 mm high, with gonothecae. New Zealand Antarctic Expedition TAN0402 [H. ovatum by Peña Cantero (2009)]: Stn 239 VV, an old, strongly polysiphonic stem, c. 22 mm high. Spanish Antarctic Expedition Bentart 2006 [H. ovatum by Peña Cantero (2013)]: Stn Low 44, several stems, up to 30 mm high; Stn Low 45, four stems, up to 17 mm high.

Diagnosis. Basally polysiphonic, slightly geniculate stems, up to 35 mm high. Stem giving rise to paired branches originating from hydrophore of primary hydrotheca. Intenodes with a characteristic long and straight basal part, followed by one or two annulations. Hydrothecae alternately arranged in one plane. Hydrotheca at the end of free hydrophore. Hydrothecal diameter strongly increasing distally; rim everted. Gonothecae flattened, bivalve-shaped, developing from hydrotheca. Cnidome consisting of microbasic mastigophores? and microbasic euryteles?

Description (type material of H. interpolatum). Stems up to 35 mm high, in very bad condition, deprived of coenosarc and overgrown by bryozoans over much of its extension. Stems slightly geniculate and weakly polysiphonic basally. Perisarc very fragile. Stems having lost most paired-branches, although their origin still visible (Figs 5 G, 8A).

Successive internodes forming at some distance below hydrothecae, which are consequently free (Fig. 8 A). Internodes with a distinct, long and straight basal part, usually interrupted distally, forming one or two rings far below hydrotheca. Internode complete in other occasions.

Hydrothecae almost completely absent and in very bad condition. Hydrotheca strongly widening distally; rim everted (Fig. 8 B).

Only one type of nematocyst could be observed.

Measurements (in µm). Hydrothecae: diameter at aperture 210–280, diameter at diaphragm 130–150, height c. 80. Cnidome: microbasic euryteles? [range 10–10.5 x 5.5–6, mean 10.3±0.3 x 5.6±0.2 (n=4); ratio, range 1.8–1.9, mean 1.8±0.1 (n=4)].

Remarks. The leptotype was designated by Rees & Thursfield (1965). Apart from Watson’s (2008) record, Halecium interpolatum has never been reported since the original description by Ritchie (1907). Apparently, however, it has been found again several times, but recorded as Halecium ovatum Totton, 1930.

After examining the type material of Halecium interpolatum, I believe that H. ovatum is conspecific with this species. The type material of the latter has not been examined because it was studied by Vervoort (1972b) and Watson (2008) who provided enough information to characterize this species. Moreover, abundant additional material (see material examined) was available from several Antarctic expeditions. Halecium ovatum agrees with H. interpolatum in the shape and size of hydrotheca, the peculiar colony structure and the cnidome. In spite of the bad condition of the leptotype, it is possible to observe the origin of paired branches as typically occurs in H. ovatum, as well as the peculiar structure of the internodes, with a long and straight basal part, usually interrupted distally and followed by one or two annulations. Ritchie (1907) already characterized this species by the presence of characteristic athecate intermediate internodes. In addition, according to Watson (2008) the cnidome of the holotype of H. ovatum includes a type of nematocyst, doubtfully considered by her as anisorhizas, of similar size (11–12 x 6–7 µm). Due to the bad condition of the type material of H. interpolatum (already pointed out by Ritchie), and the absence of coenosarc, I could observe only a few nematocysts, consisting of microbasic euryteles?

Stepanjants (1979) already pointed out the great similarity between H. interpolatum and H. ovatum in colony branching and hydrothecal constitution, indicating that the only difference was the presence of lateral stolons in the branches of H. interpolatum. It should be noted, however, that Ritchie (1907: 526) stated that “One of the branches ended in peculiar, stolon-like outgrowths”. Stepanjants (1979), finally, indicated that future studies could allow considering both conspecific. She also brought to H. ovatum and, consequently, is brought to H. interpolatum here, the material previously considered by her (Stepanjants, 1972) as H. tenellum.

Part of the material assigned to Halecium tubatum by Watson (2008), in particular the material from the slides F147470.2 and F147470.3 (see material examined), actually belong to H. interpolatum (cf. Fig. 5 H–J). Unfortunately no nematocysts were found. See the discussion below, when dealing with H. tubatum.

The material assigned to H. tenellum by Blanco (1984) also appears to belong to H. interpolatum. Peña Cantero (2013) already indicated that it could belong to H. ovatum (here considered conspecific with H. interporlatum). They agree in size and shape of the hydrothecae, the presence of paired branches and the structure of the internodes (cf. pl. 6 in Blanco 1984).

Ecology and distribution. Shelf species found at depths from three (Stepanjants 1979) to 471 m (Peña Cantero & García Carrascosa 1995). Frequently reported epibiotic on other species of hydroids (Totton 1930; Stepanjants 1979; Peña Cantero & García Carrascosa 1995; Peña Cantero 2008, 2013; Peña Cantero & Vervoort 2009), but also on algae (Peña Cantero et al. 2013), sponges (Stepanjants 1979), polychaete tubes (Totton 1930; Stepanjants 1979), and bryozoans (Peña Cantero 2013; Peña Cantero et al. 2013). Used in turn as substratum for other hydroids (Peña Cantero et al. 2013).

Gonothecae in January (Totton 1930; Stepanjants 1979; Peña Cantero et al. 2013), February (Peña Cantero 2008; Galea & Schories 2012b) and December (Stepanjants 1979).

Circum-Antarctic distribution, reported from Scotia Bay, the South Orkney Islands (Ritchie 1907), Palmer Archipelago (Vervoort 1972b), off Elephant Island (Peña Cantero & García Carrascosa 1995), Low Island (Blanco 1984; Peña Cantero & Vervoort 2009; Peña Cantero 2013), and from the South Shetland Islands (Peña Cantero 2008; Galea & Schories 2012b), in West Antarctica, and from the Ross Sea (Totton 1930; Peña Cantero et al. 2013), Commonwealth Bay, George V Coast (Watson 2008), Mawson Coast (Watson 2008 as H. tubatum), the Davis Sea (Stepanjants 1972, 1979), and the Balleny Islands (Peña Cantero 2009), in East Antarctica.