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: 9-10

publication ID 10.5281/zenodo.205235

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Sertularella  sp.

( fig. 4View FIGURE 4 H –M)

? Sertularella polyzonias  – Warren, 1908: 291, fig. 5AView FIGURE 5 –B [not Sertularella polyzonias (Linnaeus, 1758)  ].

Material examined. Stn. I10, 28.xi.2007: numerous sterile stems with hydrorhiza creeping on sponge ( NHM 2009.20).

Description. Colonies composed of erect, straight ( fig. 4IView FIGURE 4), monosiphonic stems, up to 15 mm high, arising from tortuous, anastomozing hydrorhiza, creeping on sponge surface; perisarc brown. Basal part of stems of variable length, devoid of hydrothecae; provided with 3 or more wrinkles just above origin from stolon ( fig. 4View FIGURE 4 H). Stems usually unbranched, although occasionally provided with no more than one side branch, the latter springing from below a stem hydrotheca. Stem and branches, when present, divided into rather short (425–515 µm) internodes, each with a hydrotheca distally; there are up to 35 hydrothecae per erect stem; nodes usually distinct, sloping in alternate directions, diameter 125–160 µm. First internode of a side branch generally longer (515–1160 µm) than distal ones ( fig. 4View FIGURE 4 J), and provided with 3–4 weak annuli basally. Hydrothecae alternate, one per internode, in two coplanar rows; flask-shaped, distinctly swollen on adcauline side (maximum width 220–270 µm) and constricted below aperture ( fig. 4View FIGURE 4 K). Abcauline wall straight or nearly so, 460–525 µm long; adcauline side adnate for 2/5th; free part S-shaped, convex proximally, concave distally, 335–375 µm long; adnate part slightly curved to nearly straight, 225–260 µm long; base of hydrotheca 115–135 µm wide. Aperture rhomboidal, diameter 170–185 µm, provided with 4 pointed cusps separated by shallow, rounded embayments; operculum composed of 4 triangular plates; margin generally without renovations, occasionally renovated once. Usually three internal, conspicuous projections of perisarc, one abcauline and two latero-adcauline, are found below the hydrothecal aperture ( fig. 4View FIGURE 4 M, upper figure). In some hydrothecae, two additional, smaller projections are inserted on both latero-abcauline sides ( fig. 4View FIGURE 4 M, lower figure). Hydranths badly preserved, the tentacle number and type of nematocysts could not be checked. Gonothecae absent.

Remarks. The present material fits the description, figures and measurements given by Warren (1908) for specimens originating from the Natal coast, which he erroneously assigned to Sertularella polyzonias (Linnaeus, 1758)  . The discovery of fertile material from Tristan da Cunha is necessary to ascertain whether they are conspecific. Both materials share morphological similarities with the European S. ellisii (Deshayes & Milne-Edwards, 1836)  , as described by Ramil et al. (1992), but the dimensions of the latter are comparatively larger, and point towards two distinct species.

Millard (1957) included Warren’s (1908) specimens in the synonymy of Sertularella mediterranea Hartlaub, 1901  , an opinion not shared here. Upon comparison with fertile specimens referable to Hartlaub’s (1901) species from Hyères ( France, Mediterranean), it becomes obvious that neither the Tristan specimens, nor those from Natal, share the typical feature of this species, i.e. the conspicuously elongated abcauline wall of the hydrotheca (see also Ramil et al. 1992). Moreover, the measurements of specimens from Hyères indicate that S. mediterranea  has thicker stems (diameter at node 190–240 µm) and larger hydrothecae (abcauline side 605–705 µm, free adcauline side 345–380 µm, adnate adcauline side 270–345 µm, maximum width 290–310 µm, and 250–270 µm wide at aperture) than the specimens from both Tristan and Natal. Additionally, the gonothecae of S. mediterranea  are 1555–1760 µm long and have a maximum width of 760– 850 µm, and are therefore comparatively smaller than Warren’s (1908) material. On the other hand, these dimensions corroborate well with the measurements provided by Ramil et al. (1992) for S. mediterranea  from Galicia, Spain.

Distribution. Possibly Natal, South Africa (Warren 1908).


University of Nottingham