Halecium cf. beanii (Johnston, 1838)

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 : 4-5

Halecium cf. beanii (Johnston, 1838)

( fig. 3 D)

Thoa beanii Johnston, 1838: 120 , pl. 7 figs 1–2 .

Halecium beanii – Schuchert, 2005: 615, figs 5 –6.

Material examined. Stn. T10, 15.ii.2005: one sterile colony, 5.5 cm high, with polysiphonic stem ( NHM 2009.17).

Remarks. The examined specimen is provisionally assigned to Johnston’s (1838) species on the account of its polysiphonic, irregularly branched stem. However, additional fertile female specimens are necessary to validate the present identification.

Millard (1975) observed both H. beanii and H. halecinum (Linnaeus, 1758) in South Africa, the closest location to Tristan da Cunha. She also warned about the impossibility of proper identification of these species in the absence of female gonothecae. On the other hand, Cornelius (1995a) showed that Linnaeus’ (1758) species always forms regularly pinnate colonies, while the stems of H. beanii are “imperfectly pinnate, shrubby, varied in appearance”, a conclusion partly shared by Schuchert (2005), who showed several exceptions.

Although Millard (1975) did not discuss any morphological peculiarities in the female gonothecae of H. beanii from South Africa, Schuchert (2005) showed several important differences (polygonal cross-section, 1. Torrey’s (1902) species has sessile primary hydrothecae, not terminal on branches, as illustrated by Jäderholm (1920).

increased number of eggs), rendering it distinct from the European population.

Distribution. Cosmopolitan, penetrating well into the Arctic Ocean and the coasts of Patagonia, but not into the Antarctic (Medel & Vervoort 2000). This is the first record of this species for Tristan da Cunha.

Figures

FIGURE 1. Map of the Tristan da Cunha archipelago, with the location of stations yielding hydroid material.

FIGURE 2. Typical habitats for hydroids on Tristan de Cunha. A and E: Dense Aglaophenia parvula Bale, 1882 tufts growing on wave-surged reef crest with sponges and colonial anemones. B: Silicularia rosea Meyen, 1834 and Obelia geniculata (Linnaeus, 1758) on Macrocystis pyrifera fronds. C: Antenella quadriaurita Ritchie, 1909 on vertical rock face with bryozoans, sponges and ascidians. D: Sertularella gayi (Lamouroux, 1821) and smaller hydroids growing on bedrock at 30 m. Photo courtesy of Sue Scott (A, B, C, and E) and Paul Tyler (D).

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 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).