Halecium pallens Jaderholm 1904

Halecium pallens Jäderholm, 1904

(pl. 3A, B, fig. 3G–M)

Halecium pallens Jäderholm, 1904b: 4. — Jäderholm, 1905: 12, pl. 5 figs 1–3. — Broch, 1948: 9, fig. 1. — Stepanjants, 1979: 105, pl. 20 fig. 2. — Peña Cantero, 2006: 935, fig. 3B. — Peña Cantero, 2008: 455. — Peña Cantero & Vervoort, 2009: 85, fig. 1G, H. — Peña Cantero, 2010: 766, fig. 4B.

Material examined. Stn. FSI — 25.ii.2010, PTA001 (25 m): a large, profusely branched colony broken off into two parts, the basal one 5.5 cm high, the upper one ca. 15 cm high, a single (presumably female) gonotheca found; 26.ii.2010, PTA013 (15 m): two sterile colonies, 4.4 and 5.6 cm high, respectively (MHNG-INVE-79618); 01.iii.2010, PTA028 (20–25 m): a single, sterile colony, 14.0 cm high, and a few broken fragments; 03.i.2011, S01 (35 m): an almost dead colony, broken into two parts, the basal one comprising the hydrorhiza and 8.5 cm of the stem, and the upper part 10.5 cm in height; S02 (20 m): a sterile colony, 14.5 cm high and a large, broken fragment 8.7 cm high (MHNG-INVE-79616); S10 (25 m): a sterile colony, 10.0 cm high, and several broken fragments; 04.i.2011, S27 (40 m): basal part of a dead colony, 8.2 cm high; S55 (40 m): a fragmentary, sterile colony, 8.5 cm high, with no basal part, and several broken fragments (MHNG-INVE-79617); 06.i.2011, S29 (30 m): a large (29 cm high), sterile colony composed of several profusely branched stems, hydrorhizae strongly intertwined. Stn. PAR — 07.i.2011, S08 (15 m): a single colony, 10.5 cm high, richly bearing female gonothecae with acrocysts, as well as fragments from that colony (MHNG-INVE-79619).

Description. Colonies generally profuse, almost in one plane, arising from plate-shaped hydrorhiza. Stems thick, strongly fascicled, perisarc dark brown. Branching of main stems occurring irregularly and generally basally; branching becoming quite regular above, giving the colonies a pinnate, feather-shaped appearance. Stems and branches in monosiphonic parts divided by slightly, though definitely oblique nodes, slanting in alternate directions. Internodes widening gradually from base to distal third, then more conspicuously to form the primary hydrophore and, next to it, the apophysis supporting the following internode. Length of internodes gradually decreasing from base to tip of side branches. Branches arising at bases of stem hydrothecae; often branches arising in pairs with a hydrotheca in between (fig. 3H). Primary hydrophores generally long, upwardly directed, surpassing level of distal node. Pseudodiaphragm seen in most hydrophores; considerably hypertrophied in basalmost hydrophores, often present in secondary or even tertiary hydrophores; reaching abaxial side of hydrophore as a thick belt. Hydrotheca shallow, walls straight and slightly diverging, margin clearly everted, but moderately outrolled. Hydrophores supporting regenerated hydrothecae gradually shorter distally. Only female gonothecae seen in present material; arising at base of primary hydrophores on the side branches; flask-shaped in frontal aspect, with lateral walls rather parallel in distal half, tapering gradually below into an indistinct pedicel; top flattened in unspent gonothecae, perisarc dissolved upon formation of acrocysts, leaving a large apical aperture for passage of egg mass. Gonotheca flattened in lateral view; seemingly composed of two halves "fused" along a crease line following the perimeter of gonotheca. Four to five eggs per gonotheca. Hydranths with 18–21 filiform tentacles. Nematocysts of two types (both seen undischarged): microbasic mastigophores and heteronemes of unidentified type (fig. 3M).

Distribution in Chile. Recorded only from the Strait of Magellan (present study).

World records. Circum-Antarctic (Peña Cantero 2006).