Halecium pseudodelicatulum, Peña Cantero, Álvaro L., 2014

Peña Cantero, Álvaro L., 2014, Revision of the Antarctic species of Halecium Oken, 1815 (Cnidaria, Hydrozoa, Haleciidae), Zootaxa 3790 (2), pp. 243-280 : 267-271

Halecium pseudodelicatulum sp. nov.

( Figs 2 C–D, 10A, 11)

Halecium delicatulum — Peña Cantero & Vervoort, 2009: 85, fig. 1d, e; Peña Cantero, 2013: 128, fig. 3D.? Halecium delicatulum — Peña Cantero, 2008: 454–555, fig. 1a; 2010: 766, fig. 4a.

? Halecium antarcticum — Galea & Schories, 2012b: 7 –9, fig. 2E, H.

Material examined. Spanish Antarctic Expedition Bentart 2006: Stn Low 44, numerous polysiphonic stems forming a dense mass c. 80 mm high, with female gonothecae (Holotype, MNCN 2.03/444, Museo Nacional de Ciencias Naturales, Madrid, Spain, one stem c. 70 mm high, with female gonothecae; remaining material paratypes). Stn Low 45, several polysiphonic stems, up to 60 mm high, with male gonothecae, on bryozoans.

Diagnosis. Polysiphonic, irregularly branched stems, up to 70 mm high. Branches originating from hydrophore of primary hydrotheca. Hydrothecae alternately arranged in one plane. Hydrotheca at the end of long, free hydrophore distinctly directed adcaudally and provided with pseudodiaphragm. Hydrotheca distinctly widening distally; rim everted. Up to sixth-order hydrothecae. Female gonotheca bivalve-shaped, both abcauline and adcauline walls of similar development. Aperture all distal part, from the widest part upwards. Male gonotheca of similar shape, but much smaller. Cnidome consisting of microbasic mastigophores? and microbasic euryteles?.

Description. Massive colony ( Fig. 10 A) composed of polysiphonic stems up to 70 mm high, densely growing together. Branching irregular and in several planes. Stem and branches divided into internodes by alternately arranged oblique nodes ( Fig. 11 A–B, D). Hydrothecae alternately arranged in one plane and placed at the end of long hydrophores ( Fig. 11 A–D); ratio between adcauline length of hydrophore and diameter at diaphragm 1.1–1.4. Hydrophores distinctly directed adcaudally. Abcauline side of hydrophore straight or with a slight basal convexity; adcauline side usually forming a clear concavity ( Fig. 11 C).

Hydrothecae surpassing considerably distal node of internode ( Fig. 11 A–D). Pseudodiaphragm present ( Fig. 11 A, D), particularly marked in stem internodes, less marked or even absent in branch internodes ( Fig. 11 B). Hydrotheca distinctly widening distally, rim everted ( Fig. 11 A–D). Usually, either without secondary hydrotheca or just with one; however, up to sixth-order hydrothecae observed.

Female gonothecae flattened ( Figs 2 C–D, 11E–F), but not terebratulid brachiopod-shaped. Instead Pinna bivalve-shaped, with both adcauline and abcauline sides of similar development. Aperture along entire distal portion, from the widest part upwards ( Fig. 11 E). Gonothecal walls becoming widely separated, leaving a very large aperture, when eggs go out. After releasing them, both ad- and abcauline gonothecal walls stay close together giving a scoop-shaped appearance to the gonotheca. Male gonotheca ( Fig. 11 G) similar to female one in shape, but much smaller.

Measurements (in µm). Hydrothecae: diameter at aperture 255–280, diameter at diaphragm 180–190, height 80. Hydrophore: adcauline length 200–250. Gonothecae: female, height 1030–1230, maximum diameter 1030–1070 (frontal view) and c. 450 (lateral view), diameter at aperture c. 1050 (frontal view); male, height c. 670, maximum diameter c. 610 (frontal view). Cnidome: very abundant microbasic mastigophores? with sharp ends (6.5– 7 x 1.5–2) and microbasic euryteles with rounded ends [range 5.5–6.0 x 3.0–3.5, mean 5.8±0.3 x 3.3±0.2 (n=10); ratio, range 1.6–1.8, mean 1.8±0.1 (n=10)].

Remarks. Although practically indistinguishable from Halecium antarcticum in colony structure and hydrothecal shape and size, the existence of two different species is demonstrated by the contrasting shapes of the female gonothecae. In H. antarcticum , apart from forming an external acrocyst, where eggs complete their development, the gonothecae are distinctly longer and narrower (1300–1450 µm high and 750–800 µm wide, in frontal view) than in H. pseudodelicatulum sp. nov. In addition, gonothecae are terebratulid brachiopod-shaped in H. antarcticum , with the adcauline wall not reaching the distal part of the gonotheca, but curving inwards, so that the most distal gonothecal part is convex in the abcauline side and concave in the adcauline one. By contrast, in H. pseudodelicatulum sp. nov., both ad- and abcauline sides of the gonotheca reach the distal end. In fact, the gonothecal aperture is much wider in this species (c. 1050 µm in frontal view), because it extends from the widest point upwards. In H. antarcticum , the gonothecal aperture is distinctly smaller (c. 450 µm in frontal view), occupying only some fraction of the distal part.

Since the holotype of H. antarcticum has only male gonothecae it is not possible to be sure about the assignation of the female material studied here. However, I have considered the female material from the Australian expedition to correspond with the female colony of H. antarcticum based on both geographical and cnidome grounds (see H. antarcticum ). As indicated above, the Australian material comes from the same area as the holotype of H. antarcticum , whereas the Low Island material, here referred to as H. pseudodelicatulum sp. nov., comes from the other side of Antarctica. Concerning the cnidome, in spite of the tiny differences, the size of the microbasic euryteles in the Australian material [6.9±0.7 x 3.5±0.4 (n=4)] is closer to that of the type material of H. antarcticum [6.7±0.2 x 3.2±0.2 (n=10)] than it is to the material from Stn Low 44 [5.8±0.3 x 3.3±0.2 (n=10)].

The material studied by Peña Cantero & Vervoort (2009), belongs to H. pseudodelicatulum sp. nov. It comes from the same Antarctic area and perfectly agrees with H. pseudodelicatulum sp. nov. in the shape and size of the female gonotheca (c. 1000 µm high and c. 900 µm wide in frontal view).

Similarly the material assigned to H. antarcticum by Galea & Schories (2012b) could belong to H. pseudodelicatulum sp. nov., as the putative female gonothecae are similar to those described above for this species. This material also comes from the same Antarctic area. This conclusion might also apply to the material studied by Peña Cantero (2008, 2010).

Ecology and distribution. Halecium pseudodelicatulum sp. nov. has been collected at depths from 82 (Peña Cantero 2013) to 240 m ( Peña Cantero & Vervoort 2009), epibiotic on barnacles ( Peña Cantero & Vervoort 2009) and bryozoans (Peña Cantero 2013), and basibiont of Eudendrium antarcticum ( Peña Cantero & Vervoort 2009) . Gonothecae in February ( Peña Cantero & Vervoort 2009; Peña Cantero 2013).

Halecium pseudodelicatulum sp. nov. is known for sure from off Elephant Island ( Peña Cantero & Vervoort 2009) and Low Island (Peña Cantero 2013), in West Antarctica.

Etymology. The specific name pseudodelicatulum refers to the fact that the shape of the hydrotheca in this species reminds that of H. delicatulum .

Figures

FIGURE 2. Halecium antarcticum Vanhöffen, 1910. (A) female gonotheca (lateral view); (B) acrocyst with eggs. Halecium pseudodelicatulum sp. nov. (C – D) female gonothecae showing eggs. (A – B from Stn BTC 25; C – D from type material). Scale bar: 200 µm.

FIGURE 10. Halecium pseudodelicatulum sp. nov. (A) colony. Halecium pseudoincertus sp. nov. (B) colony. (A from type material; B from holotype). Scale bar: 2 cm.

FIGURE 11. Halecium pseudodelicatulum sp. nov. (A – B, D) internodes showing hydrothecae (B with secondary hydrotheca); (C) detail of primary and secondary hydrothecae; (E) female gonotheca showing eggs (frontal view); (F) female gonotheca (lateral view); (G) male gonotheca. (A – C, E – F from type material; D, G from Stn Low 45). Scale bar: 250 µm.