Halecium incertus Naumov & Stepanjants 1962

Peña Cantero, Álvaro L., 2014, Revision of the Antarctic species of Halecium Oken, 1815 (Cnidaria, Hydrozoa, Haleciidae), Zootaxa 3790 (2), pp. 243-280 : 256-261

Halecium incertus Naumov & Stepanjants 1962

( Figs 6–7 )

Halecium incertus Naumov & Stepanjants, 1962: 98 , fig. 18; Stepanjants, 1979: 107, pl. 20 fig. 7A–V; Vervoort & Watson, 2003: 86; Peña Cantero, 2004: 769; Peña Cantero & Gili, 2006: 766.

Halecium dufresnae Millard, 1977: 8 , fig. 2A–D; 1979: 138; Branch & Williams, 1993: 11, fig.; Vervoort & Watson, 2003: 85.

Halecium macrocaulus Watson, 2008: 173 –174, fig. 9A–F.

Not Halecium incertus — Peña Cantero, 2008: 454 –455, fig. 1b; 2009: 1747; 2012: 857 (= Halecium pseudoincertus sp. nov.).

Material examined. Holotype of Halecium incertus , ZIRAS, “Ob” II SAE, Stn 204, 30–02–1957, 65° 59,2S 57°08’8E (Enderby Land), 270 m, three stem fragments, 42, 32 and 30 mm long, with gonothecae. Holotype of Halecium macrocaulus , BANZARE , Stn 107, 66°45'S 62°03'E (Mawson Coast), 210 m, one microslide, NMV F147467, one stem fragment, c. 24 mm long, with gonothecae. German Antarctic Expedition Polarstern XXI/2: Stn PS65/019, one stem, c. 195 mm high, with gonothecae.

Diagnosis. Strongly polysiphonic, irregularly branched stems, up to 300 mm high. Branches originating from hydrophore of primary hydrotheca. Hydrothecae alternately arranged in one or two planes. Hydrotheca at the end of short, adnate hydrophore provided with oblique pseudodiaphragm. Hydrotheca distinctly widening distally; rim slightly everted. Adcauline hydrothecal wall free; distinctly larger than abcauline one. Hydrothecal aperture slightly directed downwards. Up to one secondary hydrotheca present. Male gonoteca oval, elongated with distal, shallow groove. Female gonotheca flattened, terebratulid brachiopod-shaped; abcauline wall longer. Aperture at distal part. With acrocyst (one embryo). Cnidome consisting of isorhizas, larger microbasic euryteles, smaller microbasic euryteles and microbasic mastigophores.

Description (type material of H. incertus ). Three stem fragments, c. 42, 32 and 30 mm long. 42-mm-long fragment corresponding to a basal stem fragment, strongly polysiphonic, c. 3 mm in diameter, and provided with a primary branch, strongly polysiphonic too. Branches divided into internodes by alternately arranged, slightly oblique nodes.

Hydrothecae on adnate hydrophores ( Fig. 6 A–D); ratio between adcauline length of hydrophore and diameter at diaphragm 1.2–1.5. Hydrotheca low ( Fig. 6 A–D), distinctly widening from diaphragm upwards. Adcauline wall distinctly larger than abcauline one ( Fig. 6 A, D). Adcauline hydrothecal wall free to internode ( Fig. 6 A–D). Hydrothecal aperture slightly directed downwards. Hydrothecal rim slightly everted ( Fig. 6 A). Up to one secondary hydrotheca present ( Fig. 6 A). An oblique, upwards directed pseudodiaphragm present ( Fig. 6 A,D).

Two female gonothecae present, arising from hydrophore of primary hydrotheca. Gonotheca fusiform, terebratulid brachiopod-shaped, with one side shorter ( Fig. 6 E).

Measurements (in µm). Hydrothecae: diameter at aperture 260–300, diameter at diaphragm 230–250, height 35–50. Internodes: length 550–700, diameter 210–300. Gonothecae: height c. 1350, maximum diameter c. 470. Cnidome: isorhizas [range 19.0–21.5 x 6.0–8.0, mean 20.5±0.7 x 7.2±0.6 (n=10); ratio, range 2.6–3.3, mean 2.9±0.2 (n=10)], larger microbasic euryteles?, very abundant [range 15.5–18.0 x 6.0–8.0, mean 16.4±0.7 x 7.3±0.7 (n=10); ratio, range 2.0–2.7, mean 2.3±0.2 (n=10)], smaller microbasic euryteles [range 7.5–8.0 x 4.0, mean 7.8±0.2 x 4.0±0.0 (n=10); ratio, range 1.9–2.0, mean 2.0±0.1 (n=10)], and microbasic mastigophores [range 8.0–8.5 x 2.0–2.5, mean 8.3±0.2 x 2.3±0.2 (n=10); ratio, range 3.2–4.3, mean 3.7±0.4 (n=10)].

Description (type material of H. macrocaulus ). “Thickest fragments (stem or major branches) 6 mm wide at base and 200 mm long; branching profuse and irregular, originally all around stem” ( Watson 2008: 173). Apparently, branching alternate at every third hydrotheca in the material examined. Branches originating just below cauline hydrothecae. Primary branches in turn giving rise to one or two secondary branches. Stem and branches divided into internodes by little marked, alternately arranged, oblique nodes ( Fig. 6 F–H).

Hydrothecae alternately arranged in two planes. Hydrothecae resting on adnate hydrophores ( Fig. 6 F–H); ratio between adcauline length of hydrophore and diameter at diaphragm c. 1.0. Hydrotheca low and free, oblique, directed downwards ( Fig. 6 F–H). Rim everted. Hydrotheca strongly widening distally, much more at adcauline side, forming a distinct concavity ( Fig. 6 F). Adcauline hydrothecal side completely free and reaching next internode ( Fig. 6 F–H). Adcauline hydrothecal side higher than abcauline one ( Fig. 6 F–H). A distinct pseudodiaphragm present, much more marked towards adcauline side ( Fig. 6 F).

Gonothecae originating directly from lateral of hydrophore (i.e., neither pedicel nor apophysis present) ( Fig. 6 G). Gonotheca inverted pear-shaped, strongly narrowing at base and broadly rounded at distal part ( Fig. 6 I). Maximum diameter at distal fifth.

Measurements (in µm). Hydrothecae: diameter at aperture 250–270, diameter at diaphragm 220–240, height abcauline wall 30–50, height adcauline wall 50–80. Hydrophore: adcauline length 220–250. Internodes: length 630–800, diameter 250–300. Gonothecae: height c. 1420, maximum diameter c. 800. Cnidome: heteronemes (only one type could be observed since observations were made on a microslide) 15–17.5 x 5 [ 19–24 x 7–9 according to Watson (2008)].

Description (PS65/19). One branched, strongly polysiphonic stem c. 195 mm high. Stem giving rise to several strongly-developed, polysiphonic, primary branches which, in turn, form polysiphonic secondary ones.

Polysiphonic branches giving rise to lower-order branches, most monosiphonic, but some slightly polysiphonic basally. Overall, up to five-order branching observed. Branches divided into internodes by alternately arranged, slightly oblique nodes.

Hydrothecae resting on adnate hydrophores; ratio between adcauline length of hydrophore and diameter at diaphragm c. 1.3 ( Fig. 7 A–C). Hydrotheca low, distinctly widening from diaphragm upwards ( Fig. 7 A). Adcauline wall slightly larger than abcauline one ( Fig. 7 A, B). Adcauline hydrothecal wall free to internode ( Fig. 7 A). Hydrothecal aperture directed downwards. Sometimes a secondary hydrotheca present ( Fig. 7 C). An oblique, usually well-marked pseudodiaphragm present ( Fig. 7 A, C).

Female gonothecae present, arising from hydrophore. Gonotheca flattened; terebratulid brachiopod-shaped, with one side shorter ( Fig. 7 E, F), in lateral view, when immature, and fusiform when mature. In frontal view, gonotheca more or less triangular ( Fig. 7 D, G).

Measurements (in µm). Hydrothecae: diameter at aperture 245–250, diameter at diaphragm 190–220, height 35–50. Gonothecae: height 1300–1400, maximum diameter c. 500 (lateral view) and 700–780 (frontal view). Cnidome: innumerous isorhizas [range 17.5–19.0 x 7.0–8.0, mean 18.3±0.5 x 7.2±0.3 (n=10); ratio, range 2.4–2.7, mean 2.6±0.1 (n=10)], larger microbasic euryteles? [range 13.0–14.0 x 6.5–7.5, mean 13.5±0.4 x 7.1±0.4 (n=5); ratio, range 1.8–2.0, mean 1.9±0.1 (n=5)], smaller microbasic euryteles [range 6.0–7.5 x 3.0–3.5, mean 6.7±0.4 x 3.4±0.2 (n=10); ratio, range 1.9–2.2, mean 2.0±0.1 (n=10)], and microbasic mastigophore (7.5–8 x 2 –2.5).

Remarks. Stepanjants (1979) described two types of gonothecae, probably male and female. Putative male gonotheca oval, elongated with a distal, shallow groove. Female gonotheca pear-shaped, flattened, and with external acrocyst. In the material from PS65/19 there are gonothecae with acrocyst where embryo is completing its development ( Fig. 7 D) and others where embryo is little developed and still within the gonotheca with the surrounding acrocyst ( Fig. 7 E–G). Apparently, shorter side deploys to allow embryo and acrocyst to exit ( Fig. 7 D).

Naumov & Stepanjants (1962) characterized this species by the structure of the hydrotheca. They indicated that the “obliquely cut aperture with turned out edges and the presence of two diaphragms in the hydrotheca separate the new species from all the known species of the genus Halecium ”. According to these authors, the species has stems “irregularly ramified in several planes”, “with primary and secondary branches polysiphonic”. The pseudodiaphragm is oblique. Interestingly, Naumov & Stepanjants (1962) also indicated that, “considering the type of ramification, the structure of the branches and the disposal of the hydrothecae, our species appear to be related to H. arboreum Allman ”. This clearly points to a colonial structure as that found in the material here assigned to H. incertus .

Stepanjants (1979) also characterized the species by having very large colonies with thick and polysiphonic stems irregularly branched repeatedly in several planes. She also indicated that young colonies have a more ordered branching: primary branches alternately arranged, second-order ones in different planes.

Millard (1977) described as Halecium dufresnae a new species that agrees in every detail with H. incertus and, in fact, Stepanjants (1979) already considered this species conspecific with H. incertus . Millard’s (1977) material also has thick fascicled stem (up to 245 mm high), branching and re-branching irregularly, but mainly in one plane.

Although it has not been possible to re-describe the general appearance of the colony of H. macrocaulus from the material examined, according to Watson’s (2008) description it is clear that H. macrocaulus has robust, polysiphonic and much branched stems. In addition, although Watson (2008) indicated that forks arise from within a hydrotheca, in the material examined here I found only branches originating just below the cauline hydrothecae.

Watson (2008: 173) also indicated the presence of a “septum (false diaphragm) of perisarc passing diagonally through hydrophore from near junction of diaphragm with abcauline wall to adcauline wall”. This “false diaphragm” clearly corresponds with a pseudodiaphragm as it has been unequivocally demonstrated by examining the holotype material of H. macrocaulus (cf. Fig. 6 F).

Halecium macrocaulus is undistinguishable from H. incertus and it is considered here conspecific with Naumov & Stepanjants’ species. They agree in colony structure, with thick stems profusely and irregularly branched, shape and size of hydrotheca, presence of pseudodiaphragm, sessile hydrophores, and size of nematocysts. The single difference concerns the presence of acrocyst in H. incertus , not described for H. macrocaulus . However, this could be explained by the fact that the gonothecae described for H. macrocaulus are either male or female but immature. As it has been shown above, in H. incertus , it is possible to find in the same colony gonothecae with acrocyst, where an embryo is completing its development, together with others where an embryo is little developed and still within the gonotheca with the surrounding acrocyst. The shape of the gonotheca of H. macrocaulus [ Fig. 6 I; see also Figure 9 B by Watson (2008: 174)] is identical to that I found in H. incertus from Bouvet (cf. Fig. 7 D, G).

It seems clear, from the above-shown descriptions that H. incertus is characterised by having large (up to 300 mm high), thick, polysiphonic stems giving rise to also polysiphonic, lower-order branches in one or several planes. Consequently, I conclude that the material ascribed to H. incertus by Peña Cantero (2008, 2009, 2012) belongs to a different, described below, new species to science, Halecium pseudoincertus sp. nov.

Ecology and distribution. Halecium incertus has been found at depths from 15 ( Stepanjants 1979) to 693 m ( Branch & Williams 1993), on rock ( Stepanjants 1979; Branch & Williams 1993), and gravel and mud ( Stepanjants 1979). Gonothecae in April ( Millard 1977; Stepanjants 1979), November ( Peña Cantero & Gili 2006), and from December to February ( Stepanjants 1979).

Halecium incertus seems to have an Antarctic –Kerguélen distribution ( Peña Cantero & Gili 2006), having been found in both Antarctic and sub-Antarctic waters. In the latter, it is known from off Crozet ( Millard 1977; Stepanjants 1979), Kerguélen ( Stepanjants 1979) and the Marion and Prince Edward islands area ( Branch & Williams 1993). In Antarctic waters, it is known from the Sodruzestva Sea ( Naumov & Stepanjants 1962), off the Amery Ice Shelf ( Stepanjants 1979), and off Mawson Coast ( Watson 2008 as H. macrocaulus ), in East Antarctica, and off Bouvet ( Peña Cantero & Gili 2006).

Figures

FIGURE 6. Halecium incertus Naumov & Stepanjants, 1962. (A – D, F – H) internodes showing hydrothecae (A with secondary hydrotheca); (E) female gonotheca (lateral view); (I) female gonotheca (frontal view). (A – E from holotype of H. incertus; F – I from holotype of H. macrocaulus Watson, 2008). Scale bar: 250 µm (A – D, F – H), 500 µm (E, I).

FIGURE 7. Halecium incertus Naumov & Stepanjants, 1962. (A – C) internodes showing hydrothecae (C with secondary hydrotheca); (D) female gonotheca with acrocyst; (E – G) a female gonotheca in different views. (All drawings from Stn PS 65 / 019). Scale bar: 250 µm (A – C), 500 µm (D – G).

FIGURE 9. Halecium jaederholmi Vervoort, 1972. (A – E) internodes showing primary hydrothecae (D with a second-order hydrotheca; D and E showing origin of gonothecae); (F – G) female gonothecae showing eggs and hydrothecae. (All drawings from holotype). Scale bar: 250 µm (A – E), 500 µm (F – G).