Hydractinia borealis ( Mayer, 1900 )

Galea, Horia R., 2007, Hydroids and hydromedusae (Cnidaria: Hydrozoa) from the fjords region of southern Chile, Zootaxa 1597 (1), pp. 1-116 : 23

Hydractinia borealis ( Mayer, 1900)

(fig. 6D–F, pl. 1C)

Lymnorea borealis Mayer, 1900: 6 , pl. 5 figs 16–18; 1910: 154, pl. 15 figs 1–3.

Podocoryne borealis: Rees, 1941: 307 , fig. 1; Russell, 1953: 125, figs 57B, 59A, C–F, pl. 6 fig. 5; Kramp, 1959: 101, fig. 67; 1961: 67; Russell, 1970: 235; Edwards, 1972: 111, figs 4–6.

Hydractinia borealis: Schuchert, 2000: 415 ; 2001a: 9, fig. 2A–B; Bouillon et al., 2004: 63, fig. 37J–N.

Material examined. Plankton —off the Huinay Scientific Field Station, 07, 08.ii.2006, 50–0 m, several medusae ( MHNG INVE 49038).

Type locality. Eastport , Maine, USA .

Remarks. Only the medusa stage of this species has been found in the study area. A recent description of its hydroid is provided by Schuchert (2001a), based on material from Iceland. The developmental stages of the medusa were described by Rees (1941). The medusae caught from the plankton are up to 2.1 mm in height and 2.8 mm in width, and have 13–16 marginal tentacles. The fully mature medusae observed by Rees (1941) had the mouth-arms divided once or twice, so that there were 8 or respectively 16 nematocyst knobs. Some of the specimens from Chile seem to have incipient gonads, and their mouth-arms were about to undertake their first division. Cnidome:

a) microbasic euryteles on tentacles, undischarged (7.8–8.1) x (2.9–3.2) µm, discharged (6.7–7.0) x (2.1– 2.4) µm;

b) desmonemes on tentacles, undischarged (5.6–5.9) x (3.2–3.5) µm, discharged (5.1–5.4) x (2.9–3.2) µm;

c) microbasic euryteles in the mouth-arms knobs, undischarged (11.3–12.3) x (3.5–3.8) µm, discharged (9.7–10.2) x (2.9–3.2) µm.

World distribution. Both the polyp and medusa stages were recorded from the British Isles, Iceland, North Sea, Atlantic coasts of North America ( Schuchert 2001a). Additional records of the medusa are from the Strait of Magellan ( Pagès & Orejas 1999).

Records from Chile. Medusae examined here were collected from fjord Comau. Additional records are those of Palma et al. (2007) from the southern channels (between the Gulf of Corcovado and Pulluche-Chacabuco channels).