Halecium cf. delicatulum Coughtrey, 1876

Galea, Horia R., 2010, Notes on a small collection of thecate hydroids (Cnidaria: Hydrozoa) from Tristan da Cunha, south Atlantic, Zootaxa 2336, pp. 1-18 : 6

Halecium cf. delicatulum Coughtrey, 1876 (morphotype 1)

( fig. 3 E, F)

Halecium delicatulum Coughtrey, 1876: 26 , pl. 3 figs 4–5 . – Ralph, 1958 (pro parte): 334, figs 11E, H–N, 12A–K (not 12L–P = Halecium flexile Allman, 1888 ). – Schuchert, 2005: 629, fig. 12.

Material examined. Stn. T17, 06.iii.2005: two sterile stems arising from the same stolon, 3 and 8 mm high, respectively.

Description. Small colony composed of two monosiphonic, unbranched stems, arising from the same stolon. Stems geniculate, divided into long internodes by oblique nodes sloping alternately in opposite directions. Each internode with well-developed distal hydrophore, pointing upwards and surpassing level of node. Hydrothecae moderately deep, pseudodiaphragm present, margin flaring, everted, renovations common. Gonothecae absent.

Remarks. Although devoid of the characteristic female gonothecae, the present specimen fits the accepted concept of H. delicatulum , due to the geniculate appearance of stem, the morphology of internodes, hydrophores and hydrothecae, and the presence of a pseudodiaphragm. See also discussion under the next hydroid.

Distribution. Reportedly circumglobal in tropical, subtropical and boreal waters (Peña Cantero 2006). This is the first record of this species for Tristan da Cunha.

Figures

FIGURE 3. A and B: Filellum sp. (material from station Stn. I 10) – portion of colony (A); hydrotheca (B). C: Halecium sp. – four erect stems. D: Halecium cf. beanii (Johnston, 1838) – fragment of monosiphonic part of stem with origin of a side branch. E and F: Halecium cf. delicatulum (Coughtrey, 1876), morphotype 1 – portion of stem (E); hydrotheca (F). G to P: Halecium? delicatulum (Coughtrey, 1876), morphotype 2 (part) – whole colony on piece of alga (G); cross section through the stolon (H); basal part of stem (I); portion of colony (J); various branching patterns (K – M); fragment of stem showing internodes (N); various shapes of primary hydrophores (O); gonotheca arising from primary hydrophore (P). Scale bars: 50 µm (H); 100 µm (F); 200 µm (B, F, O); 300 µm (A, E, I, P); 400 µm (D, K, L, M); 500 µm (N); 2 mm (J); 1 cm (G).

FIGURE 4. A to E: Halecium? delicatulum (Coughtrey, 1876), morphotype 2 (continued) – gonotheca replacing a hydrotheca (A) or arising from stolon (B); mature female gonotheca with eggs (C); various shapes of female gonotheca (D); cross section through gonotheca (E). F and G: Amphisbetia minima (Thompson, 1879) – basal portion of stem (F); gonotheca (G). H to M: Sertularella sp. – basal part of stem (H); fragment of stem showing its straight shape (I) and mode of branching (J); two internodes (K); shape of hydrotheca (L); frontal views of two hydrothecal apertures showing 3 and 5 internal projections of perisarc (M). N and O: Sertularella gayi (Lamouroux, 1821) – fragment of monosiphonic part of stem with basal parts of three side branches (N); various shapes of the hydrotheca (O); P and R: Aglaophenia parvula Bale, 1882 – hydrotheca and detail of its margin (P); female corbula (R). S: Antennella quadriaurita Ritchie, 1909 – detail of stem in lateral (left) and frontal (right) views. Scale bars: 100 µm (M, P); 200 µm (F, S); 300 µm (A, B, E, K, L, O); 400 µm (J); 500 µm (C, D, G); 750 µm (H); 1 mm (I, R); 1.5 mm (N).

FIGURE 5. A to C: Plumularia setacea (Linnaeus, 1758) – stem internode and basal part of cladium (A); female gonotheca (B); stolonal nematothecae (C). D: Silicularia rosea Meyen, 1834 – hydrotheca (middle), female (left) and male (right) gonothecae. E: Clytia gracilis (M. Sars, 1850) – hydrotheca atop its pedicel. F: Clytia paulensis (Vanhöffen, 1910) – hydrotheca atop its pedicel. G: Obelia dichotoma (Linnaeus, 1758) – fragment of stem with hydrotheca. H: Obelia geniculata (Linnaeus, 1758) – stem internode with hydrotheca. Scale bars: 100 µm (C); 200 µm (G); 300 µm (A, B, F, H); 400 µm (E); 1 mm (D).