Halecium platythecum Galea, Försterra & Häussermann, 2014

Galea, Horia R., Schories, Dirk, Försterra, Günter & Häussermann, Verena, 2014, New species and new records of hydroids (Cnidaria: Hydrozoa) from Chile, Zootaxa 3852 (1), pp. 1-50 : 23-25

Halecium platythecum Galea, Försterra & Häussermann , sp. nov.

(Plate 2D; Figs 2 M, N; 3I, J; Table 4 )

Halecium delicatulum ―Galea, 2007: 54, Fig. 12E–H (not 12I, J = H. flexile Allman, 1888 ). not Halecium delicatulum Coughtrey, 1876a: 299 ; 1876b: 26, pl. 3 Figs 4 , 5 .

Material examined. Comau, North side of entrance to Quintupeu fjord, lat. -42.15000, long. -72.43333, 25.ii.2005, 15‒ 25 m, sample S22: part of the male colony MHNG-INVE-53175 [see Galea (2007)]. HF11, Estero Millabu, lat. -45.75762, long. -74.55160, 20.xi.2011, 7.4 m, sample C021: a female colony with monosiphonic stems, up to 3.5 cm high, on worm tube and stems of Symplectoscyphus sp. (holotype: MHNG-INVE-86251).

Description. Colonies arising from creeping, branching stolon. Stems up to 3.5 cm high, monosiphonic throughout (Pl. 2D); a few basal constrictions above origin from stolon; remainder of stem divided by oblique nodes into moderately long, geniculate internodes, the latter with two proximal annuli and a distal bulge ( Fig. 2 M). Each internode carries a well-developed, latero-distal hydrophore, reaching or slightly surpassing the level of distal node; pseudodiaphragm absent ( Fig. 2 N). Branching sparse and irregular; side branches given off singly from the hydrophores in front or rear side of the stem; basally with several oblique annuli; there are up to second order branches. Hydrothecae borne of corresponding hydrophores; moderately deep, walls divergent, rim strongly everted; renovations commonly present, up to 8; following hydrophores of varied length, the second generally well-developed and annulated basally, the next ones rather short. Most hydranths shed. Gonothecae given off from the primary hydrophores, slightly below the hydrothecal bases; pyriform in frontal view, and laterally flattened in both sexes. Female with an apical, circular aperture with thickened perisarc (Fig. 3I); male devoid of aperture (Fig. 3J). The cnidome composition could not be checked.

Remarks. This species with monosiphonic habit was previously (Galea 2007) included in the synonymy of what is now regarded as H. flexile (see above). Both species are distinguished on the following accounts: 1) H. platythecum always forms monosiphonic stems, those of H. flexile becoming readily polysiphonic in colonies less than 2 cm high, thus comparatively smaller than the largest ones in the new species; 2) the internodes of H. platythecum are geniculate, while those of H. flexile are always collinear, even in the smallest, monosiphonic stems; 3) the internodes are comparatively thicker in H. flexile ; 4) there is always a pseudodiapragm on the adaxial side of the primary hydrophores of H. flexile , while it is missing in H. platythecum ; 5) the female gonothecae of H. flexile are distinctly swollen (see Fig. 3A2) and seem to produce less oocytes than the laterally compressed gonothecae of H. platythecum .

Etymology. The specific name results from the fusion of the Greek adjective πλατύς (meaning flattened) with the substantive θήκη (meaning receptacle), in order to characterize the shape of the female gonotheca.

Distribution in Chile. Fjord Comau (Galea 2007), while the present material originates from the Millabu Strait.

World records. The distribution outside Chile could not be evaluated at present based on literature data.

Halecium tehuelchum (d’Orbigny, 1842) 14 (Plate 2E; Fig. 4 H–M)

Thoa tehuelcha d’Orbigny, 1842 : pl. 12 Figs 4 , 5 ; 1847: 25. Halecium tehuelcha— Hartlaub, 1905: 602, Fig. X2.

Halecium tehuelchum— Bedot, 1905: 80.— Blanco, 1994: 188.

Material examined. HF11, Punta Garro, lat. -46.31517, long. -75.65203, 30.xi.2011, 17.3 m, sample C349: a 4.5 cm high, male colony, on dead gorgonian (MHNG-INVE-86217); 30.xi.2011, 13.5 m, sample C351: a 5.0 cm high female colony, on worm tube (MHNG-INVE-86216).

Description. Colonies up to 5 cm high, very flaccid when out of liquid, arising from a creeping, branched, anastomosed stolon. Stems with a few annuli above origin from stolon; monosiphonic, thin, delicate, becoming less distinct in much ramified colonies; divided into internodes by oblique constrictions of the perisarc. Internodes geniculate, exceedingly long (1145–1990 µm), slender (100–140 µm wide at nodes), straight for most of their length, except for a distal bent at origin of hydrophore (Pl. 2E, Fig. 4 H1); basally with 2–4 annuli, and a short, distal apophysis supporting the following internode; hydrophores 105–185 µm long, surpassing level of distal node. Side branches arising singly or in pairs from hydrophores, just below the hydrothecal diaphragms, and oppositely to the direction taken by the next stem internodes; structure like the stem ( Fig. 4 H3). Hydrotheca 50–60 µm deep, distinctly flared (85–105 µm wide at base and 120–170 µm at aperture), rim everted ( Fig. 4 I); a ring of desmocytes above diaphragm; no pseudo-diaphragm. Hydrothecae often regenerated (up to 4 times), especially those at the end of a side branch; length of secondary, tertiary etc. hydrophores generally decreasing distally. Female gonothecae arising from within the hydrothecae ( Fig. 4 J1); 1010–1290 µm long and 770–925 µm wide, broadly rounded to irregular in shape, laterally flattened ( Fig. 4 J3), aperture distal, circular, 110–145 µm in diameter; oocytes 105–120 µm wide, their number could not be ascertained in these partly spent gonothecae, though up to 8 could be seen in the best preserved ones. Male gonothecae arising laterally from below the hydrothecal bases or, more rarely, from within the hydrothecae; smaller than female (780–1120 µm long, 380–415 µm wide), elongated-ovoid, and also

14. D’Orbigny not only dated his species using the date of the writing of his manuscripts, but his work was issued in livraisons, many of them consisting of solely plates ( Sherborn & Woodward 1901). According to Sherborn & Griffin (1934), the name becomes available with the publication of the plates in 1842, the text appearing later in 1847. Additional species described by d’Orbigny, such as the well-known Symplectoscyphus milneanus , have been dated 1846 in numerous earlier accounts, and should consequently be dated correctly 1842.

laterally flattened. Cnidome ( Fig. 4 M): small [(6.3–6.9) × 2.6 µm] and large (ca. 9.8 × 4.0 µm) heteronemes (none seen discharged), as well as microbasic mastigophores [(6.0–6.6) × 1.7 µm].

Remarks. The characteristic habit of the colony is well illustrated by d’Orbigny (1842, Pl. 12 Fig. 4 ), while the structure of the stem, though in almost good agreement with the specimens observed by us, fails to show the hydrothecae (d’Orbigny’s Pl. 12 Fig. 5 ). The sex of the gonotheca drawn by d’Orbigny could not be ascertained with certainty, and differs from both male and female gonothecae in the present material, in having a wide aperture. The latter may have been expressly exaggerated by d’Orbigny, since no other Halecium species displays such wide apertures, neither in females nor in males.

Blanco (1994) doubted the identity of this hydroid, and the present record represents the second finding of this species.

Distribution in Chile. The present record is from a locality situated at about 46°S.

World records. Previously known only from near the mouth of Río Negro, Argentina, which is the type locality (d’Orbigny 1842).

Figures

FIGURE 2. A, B: Halecium flexile Allman, 1888 — portion of stem (A) compared with H. balei Fraser, 1911 (C); detail of hydrophore and renovated hydrotheca (B), and comparison with H. balei (D). E, F: Halecium humeriformis sp. nov. — stem fragments (E); hydrophore and renovated hydrotheca (F). G, H: Halecium maximum sp. nov. — stem fragments (G); hydrophore and renovated hydrotheca (H). I ‒ L: Halecium modestum sp. nov. — stem fragments (I ‒ K); hydrophore with hydrotheca (L). M, N: Halecium platythecum sp. nov. — stem fragment (M); hydrophore and renovated hydrotheca (N). Scale bars: 300 µm (B, D, F, H, L, N) and 1 mm (A, C, E, G, I ‒ K, M).

FIGURE 4. A ‒ F, M: Cnidomes of some Halecium species discussed herein— H. flexile Allman, 1888 (A); H. balei (B); H. humeriformis sp. nov. (C); H. maximum sp. nov. (D); H. tristaniensis sp. nov. (E); H. modestum sp. nov. (F). G: Halecium pallens Jäderholm, 1904 — female gonotheca. H ‒ M: Halecium tehuelchum (d’Orbigny, 1842) — fragments of colonies (H), primary hydrophore and renovated hydrotheca (I); female gonotheca (J) and shape variation (K); male gonothecae (L); cnidome (M). Scale bars: 10 µm (A ‒ F, M); 300 µm (I, J, L), 500 µm (G, K), 1 mm (H).

FIGURE 5. A ‒ E: Hydrodendron chilense sp. nov. — colonies and fragments (A); hydrotheca (B); nematothecae (C); male gonotheca (D); cnidome (E). F ‒ K: H. mirabile (Hincks, 1866) from the Mediterranean—colony (F); hydrothecae (G) and nematothecae (H); male (I) and female (J) gonothecae; cnidome (K). L ‒ P: H. mirabile from Martinique—four colonies (L); hydrothecae (M) and nematothecae (N); male gonotheca (O); cnidome (P). Q: Hydrodendron sp. from Guadeloupe—cnidome. Scale bars: 10 µm (E, K, P, Q), 200 µm (B, C, G, H, M, N), 300 µm (D, I, J, O), 500 µm (A, F, L).