Halecium brevithecum Watson, 2008

Peña Cantero, Álvaro L., 2014, Revision of the Antarctic species of Halecium Oken, 1815 (Cnidaria, Hydrozoa, Haleciidae), Zootaxa 3790 (2), pp. 243-280 : 251-253

Halecium brevithecum Watson, 2008

( Fig. 4 A–C)

Halecium brevithecum Watson, 2008: 168 –169, fig. 4A–C.

Material examined. Holotype, BANZARE Stn 41, 65°48'S 53°16'E (Enderby Land), 209 m, NMV F147457, one microslide with a few stem fragments (longest c. 15 mm long).

Diagnosis. Large, reddish, polysiphonic, irregularly branched stems. Branches originating either from abcauline side of hydrophore of primary hydrotheca or from inside hydrotheca. Usually, with ahydrothecate intermediate internode after apophysis. First hydrothecate branch internode distinctly longer. Hydrothecae alternately arranged in one plane. Hydrotheca at the end of short, adnate hydrophore. Hydrotheca very slightly widening distally; rim not everted. Adcauline hydrothecal wall adnate to internode. Hydrothecal aperture slightly directed downwards. No secondary hydrothecae present. Gonothecae unknown. Cnidome consisting at least of microbasic euryteles?

Description. Thick, reddish stems. “Stem or branch fragments of a presumably larger colony. Stem (branch) fascicled, polysiphonic tubes varying from knotted to parallel. Branching irregular, ultimate branches monosiphonic” ( Watson 2008: 169). Stem and branches divided into relatively short and thick internodes by alternately arranged, slightly oblique nodes ( Fig. 4 B, C). Branches originating either just below hydrotheca on abcauline side (secondary branch more or less perpendicular to old one) or, more frequently, from inside hydrotheca. Usually, with ahydrothecate intermediate internode following apophysis ( Fig. 4 A). First hydrothecate internode of branch distinctly longer ( Fig. 4 A).

Hydrothecae alternately arranged in approximately one plane. Hydrothecae low ( Fig. 4 A–C), placed at end of adnate hydrophores; ratio between adcauline length of hydrophore and diameter at diaphragm 0.7–1.0. Hydrotheca very slightly widening distally. Adcauline wall much higher than abcauline one, extending upwards on internode ( Fig. 4 A–C). Adcauline hydrothecal wall adnate to internode. Hydrothecal aperture slightly directed downwards ( Fig. 4 A–C). No secondary hydrothecae present.

Measurements (in µm). Hydrothecae: diameter at aperture 215–225, diameter at diaphragm 200–215, height 20–25. Hydrophore: adcauline length 130–200. Internode: length 640–1240, diameter 230–350. Cnidome: microbasic euryteles? (only one type could be observed), c. 12.5 x 5.

Remarks. The overall colony form is not yet known. According to Watson (2008: 169) branches “given off from side of a hydrophore; branches beginning with three to five deeply indented transverse nodes, internodes thereafter moderately long”. As stated above, in the holotype, branches more frequently arise from within the hydrothecae.

Watson (2008) stated that the adnate hydrophore becomes free just below the hydrotheca. However, in the material examined, the hydrophore is completely adnate. In fact, as stated above, the adcauline hydrothecal wall is also adnate to the internode [as it was also pointed out by Watson (2008)], and, consequently, there is no way for the hydrophore to be partially free.

Halecium brevithecum was described from very scarce, infertile material, most mounted into microslides. Because of this, H. brevithecum cannot be completely characterized. The gonothecae are unknown and the cnidome information is practically non-existent (I could observe only one nematocyst). Halecium brevithecum is similar to H. jaederholmi and H. secundum (see below for a discussion about the differences with those species).

Ecology and distribution. Halecium brevithecum is known from depths between 209 and 502 m, off Enderby Land and Knox Coast ( Watson 2008).

Figures

FIGURE 4. Halecium brevithecum Watson, 2008. (A – C) internodes showing primary hydrothecae (A with basal ahydrothecate intermediate internode). Halecium secundum Jäderholm, 1904. (D – F) internodes showing primary hydrothecae. (All drawings from type material). Scale bar: 250 µm.