Hydractinia parvispina Hartlaub, 1905

Galea, Horia R. & Schories, Dirk, 2012, Some hydrozoans (Cnidaria) from Central Chile and the Strait of Magellan, Zootaxa 3296, pp. 19-67 : 25-26

Hydractinia parvispina Hartlaub, 1905

(fig. 2A–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).