( Fig. 2 E, H)
Halecium antarcticum Vanhöffen, 1910: 318, fig. 34. — Billard, 1914: 7, fig. 5. — Totton, 1930: 144, fig. 4.
? Halecium antarcticum — Watson, 2008: 166, fig. 2.
? Halecium gracile — Billard, 1906: 10 (not H. gracile Bale, 1888).
Halecium delicatulum — Naumov & Stepanjants, 1962: 94, fig. 16. — Stepanjants, 1972: 72; 1979: 105, pl. 20 fig. 4 A. —Peña Cantero, 2006: 937, fig. 3 C. — Peña Cantero & Gili, 2006: 766. — Peña Cantero, 2008: 454, fig. 1 A. — Watson, 2008: 169, fig. 5 A, B. — Peña Cantero & Vervoort, 2009: 85, fig. 1 D, E. — Peña Cantero, 2010: 766, fig. 4 A (not H. delicatulum Coughtrey, 1876).
not Halecium delicatulum —Blanco & Bellusci de Miralles, 1972: 7, pl. 1 figs 3–5. — Vervoort, 1972 b: 341, fig. 2 A. — Blanco, 1984: 7, pl. 4 figs 8–11, pl. 5 figs 12, 13. — Watson, 2008: 169, fig. 5.
Material examined. Stn. SHO — 23.ii. 2011, Ant. 23 / 2011 ( 20–30 m): two small stems, 6 and 5 mm high, respectively, the latter bearing a presumably female gonotheca (content badly preserved).
Remarks. It is likely that the binomen Halecium delicatulum Coughtrey, 1876 was used as a common denominator for several haleciid hydroids from various oceans, characterized by mono- or polysiphonic stems (age-dependent), with more or less geniculate internodes, moderately long primary hydrophores provided with a pseudodiaphragm on the adaxial side, hydrothecae with distinctly everted rim, and ovoid, more or less laterally flattened gonothecae. The taxonomy of this possible complex of species is far from settled. In spite of this evidence, several authors regarded Coughtrey's species as a cosmopolitan taxon ( e.g. Watson 2008), whose geographical distribution spreads even to Antarctica (Peña Cantero 2006).
A discussion on the morphological variability and the specific limitation of H. delicatulum was provided by Galea ( 2010), who re-examined the New Zealand material (microslide MNHG-INVE- 26669) described by Schuchert ( 2005). The gonothecae from Wellington are provided with two prominent "ears" flanking the aperture ( Fig. 2 I), a very characteristic feature also underlined by Ralph ( 1958). Moreover, they are notably smaller than the gonotheca found in our present Antarctic material ( Fig. 2 H). Additionally, the internodes of H. delicatulum are more slender and more geniculate ( Fig. 2 G), and the primary hydrophores, as well as their corresponding hydrothecae ( Fig. 2 F), are of smaller proportions compared to the specimen assigned here to H. antarcticum ( Fig. 2 E).
Accordingly, we suggest avoiding the use of the binomen H. delicatulum for Antarctic haleciids unless it is indisputably shown that their female gonothecae are morphologically identical to those described in New Zealand specimens, the latter being thought to illustrate the accurate concept of Coughtrey's species. It is also worth mentioning that the relationship between H. antarcticum and H. flexile Allman, 1888 is still unsettled, and both may prove conspecific, an opinion already expressed by Totton ( 1930) and shared by us.
The specimens with very long primary hydrophores assigned by Blanco & Bellusci de Miralles ( 1972), Vervoort ( 1972 b), and Watson ( 2008) to H. delicatulum, as well as those included by Blanco ( 1984) in H. antarcticum, may not belong to the present species [partly suggested earlier by Peña Cantero ( 2006)]. Moreover, the gonotheca described by Watson ( 2008) for H. antarcticum is peculiar, being provided with a "low apical dome with flattened top", a feature not met with in specimens discussed in earlier accounts.
Geographical distribution. Unknown with certainty in the absence of a more comprehensive, comparative study based on a relevant number of fertile (female) specimens from both Antarctic and sub-Antarctic localities.