Thuiaria longstaffi, Hickson & Gravely, 1907

Soto, Joan J. & Peña, Álvaro L., 2019, Benthic hydroids (Cnidaria, Hydrozoa) from the Weddell Sea (Antarctica), Zootaxa 4570 (1), pp. 1-78 : 15

Tubularia longstaffi Hickson & Gravely, 1907

( Fig. 4 a–i)

Material examined. ANT XVII/3: 111-5, few stems, up to 45 mm high, on O. terranovae ; 111-7, some stems, up to 40 mm high, with developing gonophores; 111-9, some stems, up to 110 mm, with mature gonophores.

Remarks. The specimens examined here concurs with all the diagnostic features mentioned in the redescription of the type material of T. longstaffi by Peña Cantero (2017): yellow stems, in entwined clusters, tube diameter increasing distally ( Fig. 4a ), with transversal ridges; polyps large, up to 5 x 5 mm, with an oral crown of 29–37 tentacles and an aboral one of 12–19 tentacles; type and size of nematocysts, and gonophores as cryptomedusoids ( Fig. 4d , g–h).

Additional knowledge regarding sexual dimorphism and early developmental stages is drawn from the present study. Male blastostyles elongate, c. 4 mm long and with up to 17 stalked gonophores as cryptomedusoids ( Fig. 4c ). Gonophore maturity increasing distally: recently formed gonophores located proximally, spherical, c. 300 µm in diameter, and completely filled with spermatogenic tissue (reddish in preserved specimens); mid-term gonophores, c. 600 µm in diameter, filled for 2/3 to 3/4 with spermatogenic tissue, with 4–5 rudimentary tentacular bulbs and slightly protruded aperture ( Fig. 4c ); fully grown male gonophores located distally, spherical, c. 1 mm in diameter, almost completely filled with whitish sperm cells between aperture and spermatogenic tissue, rudimentary tentacular bulbs difficult to appreciate at this stage ( Fig. 4d ). Female blastostyles elongate, up to 7 mm long, and with up to 11 stalked gonophores as cryptomedusoids, fully matured ones scattered along the blastostyle ( Fig. 4f ). Developing gonophores sphaerical, c. 250–600 µm; fully grown female gonophores oblong in lateral view, c. 1.5 mm wide x 1 mm high, with a digitiform process running on proximal section, with 4–5 rudimentary tentacular bulbs, and with up to four actinulae, of which 2–3 developing and 1–2 mature ( Fig. 4 g–h). Actinula resembling a Tubularia polyp, with 10 elongate aboral tentacles and four short oral ones. Basal section dense, with two constrictions, one at the base of aboral tentacles, the other at the basal fourth, delimiting a disc. Basal disc with radial grooves, probably with adhesive function ( Fig. 4i ).

Cnidome composed by small stenoteles [range 9.0–11.0 x 7.0–8.5 µm, mean 10.1±0.7 x 7.8±0.6 µm (n=18)], large stenoteles [range 14.0–15.5 x 10.0–12.5 µm, mean 14.4±0.4 x 10.7±0.7 µm (n=17)], tear-shaped haplonemes [range 13.5–16.5 x 4.0–5.5 µm, mean 14.9±1.1 x 4.9±0.6 µm (n=16)], rounded haplonemes [range 15.5–16.5 x 10.0–11.5 µm, mean 16.0±0.5 x 10.9±0.5 µm (n=15)] and desmonemes [range 5.5–7.0 x 4.0–6.0 µm, mean 6.4±0.6 x 4.8±0.6 µm (n=16)].

Ecology and distribution. Tubularia longstaffi was only known from the Ross Sea ( Hickson & Gravely 1907; Peña Cantero 2017), reported at depths between 222 and 630 m (Peña Cantero 2017); present material was collected at 62–67 m depth, in the vicinity of Cape Norvegia. This constitutes the third record of the species, and the first evidence from both the Weddell Sea and West Antarctica. We tentatively assign a circum-Antarctic distribution to T. longstaffi .

Figures

FIGURE 4. a–i Tubularia longstaffi: a polyp-carrying tube; b male polyp; c blastostyle with developing male gonophores; d blastostyle with fully-grown male gonophores; e female polyp; f blastostyle with fully-grown female gonophores; g–h detail of female gonophores carrying actinulae; i actinulae in different stages of development. j–o Zanclea hicksoni: j early-developing polyp, k expanded young polyps, l expanded polyps with hydrorhizal filaments, m contracted polyp, n–o detail of polyps showing tentacle arrangement in linear clusters (arrows).