Halecium modestum Galea & Schories

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 : 22-23

Halecium modestum Galea & Schories , sp. nov.

(Plate 2C; Figs 2 I–L; 3H; 4F; Table 4 )

Material examined. Niebla, Bonifacio, lat. -39.68333, long. -73.36667, 07.viii.2012, 12 m, sample 02: a 2.5 cm high male colony (paratype: MHNG-INVE-86214). Corral, Chaihuin/Huiro, lat. -39.95000, long. -73.61667, 03.x.2011, 8‒ 12 m, sample 19: several colonies up to 4 cm high, some male and some female, on sponge (paratype: MHNG-INVE-86211); 03.x.2011, 10 m, sample 26: a 3 cm high male colony on sponge (paratype: MHNG-INVE- 86213); 17.x.2011, 8 m, sample 22: a 3 cm high female colony on sponge and bryozoan (paratype: MHNG-INVE- 86212); 16.xi.2011, 8‒ 10 m, sample 03: a 6 cm high colony with some stems bearing female gonothecae, mostly immature (holotype: MHNG-INVE-86210); 16.xi.2011, 8‒ 10 m, sample 05: a 3 cm high sterile colony on sponge (paratype: MHNG-INVE-86215).

Description. Colonies bushy, up to 6 cm high (Pl. 2C), arising from rhizoid stolons. Stems and side branches polysiphonic. Distal, monosiphonic parts composed of a succession of moderately long, geniculate internodes, each with a bulge at both ends, as well as with a long, latero-distal hydrophore, greatly surpassing the level of distal node ( Fig. 2 I–K); hydrophores given off alternately on successive internodes, each with a pseudodiaphragm on adaxial side ( Fig. 2 L). Hydrothecae with everted rim; renovations common. Side branches given off singly from either sides of the primary hydrophores ( Fig. 2 I), occasionally from within the hydrotheca ( Fig. 2 J); additional branches originate from the auxiliary tubes running up the stems; major branches arising irregularly and in all planes, and generally set at acute angles with the stem. More numerous, relatively short branchlets, composed of only one or two internodes, are given off throughout the colony from the primary hydrophores, giving the stem and main branches a bottle brush appearance. Some other branchlets form tendrils distally, that anastomose with those of the neighbouring stems. Gonothecae borne of primary hydrophores, below the hydrothecal bases; male and female similar in frontal view, the former comparatively more flattened laterally and devoid of aperture; fertilization may occur inside the female gonotheca at least up to the blastula stage, as shown in Fig. 3H4. Cnidome ( Fig. 4F ): small [(5.7–6.0) × (2.9–3.1) µm] and large [10.3–10.6) × (4.6–4.9) µm] heteronemes (none seen discharged), microbasic mastigophores [(6.0–6.3) × 1.7 µm].

Remarks. The typical mode of branching of H. modestum is also shared by H. maximum sp. nov. (see above), but there are several important features that distinguish both species: 1) the colonies of H. maximum are comparatively larger and more robust than those of H. modestum (up to 9 cm vs. generally 3–4 cm, exceptionally 6 cm, as on Pl. 2C); 2) their stems are invested only basally by a reduced number of secondary tubes, while both stems and branches of H. modestum are highly polysiphonic; 3) the gonothecae of both sexes of H. maximum are much bigger than those of the present species (see Table 4 ); 4) there are 12–13 large (230–305 µm wide) oocytes in the female gonotheca of H. maximum , while up to 9, smaller (195–235 µm wide) cells are produced by H. modestum ; 5) unlike H. modestum , the male gonothecae of H. maximum are provided with a well-defined aperture, like the females (Fig. 3F); 6) both the small and large heteronemes of H. modestum exhibit much swollen capsules than their respective counterparts in H. maximum (compare Fig. 4F and 4D ).

Etymology. From the Latin modestus (-a, -um), with reference to its moderately high, less luxuriant colonies, and smaller gonothecae compared to those of the preceding species.

Distribution in Chile. Only known from the Valdivia area (present study).

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).