Halecium humeriformis 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 : 19-20

Halecium humeriformis Galea & Schories , sp. nov.

( Figs 2 E, F; 3D; 4C, Table 4 )

? Halecium gracile ― Jäderholm, 1903: 266, pl. 12 Figs 2 , 3. not Halecium gracile Bale, 1888: 759 , pl. 14 Figs 1 –3.

Material examined. Taltal, lat. -25.38333, long. -70.51667, 24.iv.2012, 12‒ 20 m, sample 27: numerous stems, up to 9 mm high, on bryozoan covered barnacle, with male and female gonothecae (holotype: MHNG-INVE-86222); sample 50: numerous female stems, up to 8 mm high, on barnacle (paratype: MHNG-INVE-86223).

Description. Stems monosiphonic, scarcely branched, up to 9 mm high, arising from creeping, branching hydrorhiza. A constriction above origin from stolon, then stem broken up into slightly geniculate to almost collinear internodes, each of which of moderate length, with bulges at both ends, and a latero-distal hydrophore supporting a terminal hydrotheca ( Fig. 2 E1, 3). Hydrophores long, with a pseudodiaphragm on adaxial side; hydrotheca deep, with everted margin; renovations common ( Fig. 2 F). Side branches, when present, given off singly from the primary hydrophores ( Fig. 2 E2); structure identical to the stem. Gonothecae arising from the primary hydrophores, from within the primary hydrotheca, or as a replacement of it, as well as from the stolon. Female laterally flattened, broadly ovoid in frontal view, tapering abruptly below into short pedicel; distally there are two lateral, earlike outgrows, in the middle of which there is a circular, notched aperture (Fig. 3D1–3). Male gonothecae ovoid, borne of short pedicel (Fig. 3D4). Cnidome ( Fig. 4C ): small heteronemes [(3.1–3.4) × 1.7 µm], microbasic mastigophores [(5.7–6.0) × 1.7 µm], and conspicuously curved heteronemes [(8.3–9.2) × 2.3 µm].

Remarks. Male and female stems are found together on the same substrate, a barnacle, but, since the latter is overgrown with an encrusting bryozoan, it is impossible to check whether the same stolon unites stems of both sexes.

The female gonotheca of H. humeriformis resembles that of the South African material assigned by Millard (1957) to a new variety, magnum, of H. parvulum 12 Bale, 1888. However, her material has much larger dimensions compared to ours. It seems therefore justifiable, as already remarked by Schuchert (2005, p. 630), to raise this variety to species, as H. magnum Millard, 1957.

The cnidome of the new species includes a peculiar, large, banana-shaped heteroneme ( Fig. 4C ), and therefore differs from the homologous capsules found in the other species described herein. It will be shown below that another congener, H. tristaniensis sp. nov., possesses an unusual capsule, too, suggesting that the knowledge of the cnidome in haleciids may represent a useful tool for discriminating between the species.

Etymology. The specific name is a fusion between two Latin words, viz. humerus (pl. -i), meaning shoulder(s), and forma (meaning shape), making reference to the latero-distal diverticles of the female gonotheca.

Distribution in Chile. Only known from Taltal (present record).

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 1. A, B: Hebella cf. scandens (Bale, 1888) — hydrotheca (A); gonotheca (B). C ‒ D: Hebella striata Allman, 1888 — hydrotheca (C); gonotheca (D). E, G, H: Phialella? falklandica Browne, 1902 — portion of erect stem (E) compared with that of P. quadrata (Forbes, 1848) (F); gonotheca seen laterally (G) and apically (H), compared with those of P. quadrata (I, stolonal; J, borne of stem). K, L: Silicularia? bilabiata (Coughtrey, 1876) — two hydrothecae (K); female gonotheca (L). M ‒ O: Silicularia rosea Meyen, 1834 — two hydrothecae (M) compared with specimens from Tristan da Cunha assigned to S. hemisphaerica (Allman, 1888) (P); female (N) and male (O) gonothecae, compared to homologous gonothecae (Q and R, respectively) from Tristan. S: Halecium corrugatissimum Trebilcock, 1828 — small stem with female gonotheca. Scale bars: 300 µm (A, B, E, F, S), 500 µm (C, D, G ‒ J), and 1 mm (K ‒ R).

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).