Halecium pallens Jaderholm 1904

Halecium pallens Jäderholm, 1904

(Fig. 4 G)

Halecium pallens — Galea & Schories, 2012a: 36, pl. 3A, B, Fig. 3G–M.— Peña Cantero, 2014: 266, Fig. 3E–K.

Material examined. Punta Arenas, lat. -53.75000, long. -70.96667, 07.i.2011, 15 m, sample S08: a single colony, 10.5 cm high, bearing female gonothecae with acrocysts, as well as fragments from that colony (MHNG-INVE- 79619).

Remarks. In a recent paper, Peña Cantero (2014) questioned the identity of a hydroid previously assigned to H. pallens by two of us (Galea & Schories 2012a). This prompted us to reexamine our material with female gonothecae (part of MHNG-INVE-79619), in order to compare it with the redescription of the holotype. After careful examination, we found that a short, terminal funnel could be noted in certain gonothecae whose acrocysts were removed manually (Fig. 4 G), while a wide open aperture is present in others.

In the first case, it appears that a thin, outer layer of the apical perisarc of the gonotheca is ruptured, while the terminal funnel is attached to the remaining, inner layer. In the second situation, it seems that the gonothecae are in a more advanced stage of maturation of their acrocysts, the latter likely contributing to the disappearance of the apical perisarc, possibly through biochemical digestion, leaving a wide open aperture.

The size of the gonothecae in our material [(1575–1705) × (620–815) µm] does not differ much from that of the holotype, as described by Peña Cantero. Taken together, the features of the female gonotheca demonstrate that our earlier identification is correct. Two additional points invoked by Peña Cantero, viz. the absence of a pseudodiaphragm in the hydrophores and the lack of a crease line along the perimeter of the gonotheca are, in our opinion, of minor importance. As already stated by Galea & Schories (2012a), the pseudodiaphragm was generally present, though inconstantly seen, among the rather abundant material from Chile. As for the crease line, this was observed only in the best preserved specimens that have not been submitted to osmotic shocks.