Halecium beanii Johnston 1838

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.