(fig. 2 A–C)
Hydractinia parvispina Hartlaub, 1905: 518, fig. A. — Jäderholm, 1905: 5, pl. 3 figs 4, 5. — Jäderholm, 1917: 4. —? Millard, 1971: 402, fig. 4. — Stepanjants, 1979: 14, pl. 1 fig. 8. — Branch & Williams, 1993: 7, fig. — Schuchert, 1996: 44, fig. 23. not Hydractinia parvispina — Ralph, 1953: 63, fig. 1.
Material examined. Stn. FSI — 01.iii. 2010, PTA033 (4 m): a female colony on gastropod shell (MHNG-INVE- 79601).
Description. Hydrorhiza crust-like, covered with naked coenosarc; spines chitinous, simple, rather conspicuous. Polyps dimorphic, with gastro- and gonozooids; the former elongate, tubular, with up to 13 filiform tentacles; gonozooids slightly smaller, with up to 12 tentacles; tentacles in one whorl, possibly amphicoronate in life; hypostome dome-shaped. Available colony female; one to eight gonophores per gonozooid, in one whorl, a short distance below tentacles; each gonophore with up to 8 nearly spherical eggs. A few gonozooids devoid of hypostome and tentacles (possibly reproductive exhaustion). Nematocysts (seen undischarged: desmonemes (5.7– 6.1)×(3.1–3.4) µm; and two size classes of microbasic euryteles, (7.7 –9.0)×(2.7 –3.0) µm and (10.1–11.4)×(3.4– 4.1) µm, respectively.
Remarks. Due to the varied degree of contraction in our fixed material, the real size of the polyps could not be determined. The number of tentacles was ascertained in a restricted number of less contracted individuals, and should not be taken as absolute. Hartlaub (1905) mentioned 15 and 11 tentacles in the gastro- and gonozooids, respectively.
Millard's (1971) material from Marion Island agrees partly with the present specimen: there are differences in the number of tentacles (11–16 and 4–6 in gastro- and gonozooids, respectively), the cnidome composition (two types of capsules instead of three), as well as the selection of a different substrate for the colony ("on stones under rocks in the lower littoral region").
Distribution in Chile. Picton Island (Hartlaub 1905), Strait of Magellan (present study).
World records. Falkland Islands (Hartlaub 1905), Graham Land (Jäderholm 1905), South Georgia (Jäderholm 1905, 1917),? Marion Island (Millard 1971). The New Zealand record by Ralph (1953) is doubtful, as explained by Schuchert (1996).