(fig. 18E–J, table 31)
Synthecium robustum Nutting, 1904: 136, pl. 41 figs 4–6; Hartlaub, 1905: 673, fig. H 5; Fraser, 1944: 236, pl. 49 fig. 221; Blanco, 1976: 51, pl. 6 figs 3–5, pl. 7 figs 1–3; Vervoort, 1972a: 193, figs 65, 66, 68A; Leloup, 1974: 24, fig. 19; Stepanjants, 1979: 101, pl. 16 fig 5A–B; El Beshbeeshy, 1991: 121, fig. 28; Blanco et al., 2000b: 293, figs 17–19.
Synthecium chilense Hartlaub, 1905: 671, figs E 5 –G 5.
Material examined. Stn. CHL 02 —04.iii.2005, 13– 20 m, S2: eight fertile stems, up to 5.5 cm high, some poorly preserved, 1 slide (MHNG INVE 53155). Stn. AIN – 11.iii. 2006, 25 m, S111: one sterile colony, 3.1 cm high (MHNG INVE 53362). Stn. CCO — 09.iii.2006, S144 (18 m): several fertile fragments, abundantly overgrown by other hydroids; S140 (0–20 m): a poorly preserved colony, 3.5 cm high, with remnants of gonothecae. Stn. CPI — 07.iii.2006, S118 (20 m): one sterile colony, 7 cm high (MHNG INVE 53374); S121 (24 m): several sterile stems, up to 7.5 cm high, and smaller fragments (MHNG INVE 53378).
Type locality. Strait of Magellan, 52°41' S, 69°55.5' W.
Description. Stems erect, monosiphonic, unbranched, up to 7.5 cm high, arising from a creeping stolon. Stems compressed on both anterior and posterior sides. Most basal part undivided and generally devoid of hydrothecae or having several damaged hydrothecae and apophyses with broken branches; remainder of stem divided by transverse nodes into internodes, each with three pairs of hydrothecae and a pair of apophyses arising below second pair of hydrothecae. Up to 16 side branches per stem, borne on their corresponding stem apophyses; opposite and pinnately arranged in same plane. Stem and branches with hydrothecae in opposite pairs, forming two longitudinal rows. There is one unpaired hydrotheca in proximal part of each side branch, followed by first pair of subopposite hydrothecae; next pairs opposite; up to 9 pairs per branch. Hydrothecae partly embedded in hydrocaulus; cylindrical, distal part curving outwards (angle of opening at about 45°); hydrothecal rim lower on lateral sides, circular, slightly everted, renovation of margin very frequent. Gonothecae arising directly from aperture of most basal stem hydrothecae and borne on short pedicel; pear-shaped, with up to 9 deep, transversal ridges in distal part, slightly marked towards basal part; gonothecal aperture circular. Gonothecae generally empty, no intact contents have been seen.
Remarks. I follow Vervoort (1972a) by including Synthecium chilense Hartlaub, 1905 in the synonymy of S. robustum Nutting, 1904.
Hydroid epibionts. Eudendrium cf. nambuccense Watson, 1985; Modeeria rotunda (Quoy & Gaimard, 1827); Sertularella robusta Coughtrey, 1876; Symplectoscyphus subdichotomus (Kirchenpauer, 1884); Symplectoscyphus sp.
World distribution. Argentina, Strait of Magellan, Falkland Islands, Tierra del Fuego, Antarctica (Vervoort 1972a).
Records from Chile. Previously reported from Calbuco (Hartlaub 1905), Golfo de Ancud and Seno Reloncavi (Leloup 1974). The present material was found roughly between 43°10' S and 50°50' S.