Campanularia hicksoni Totton 1930

Campanularia hicksoni Totton, 1930

(Fig. 7 e–h)

Material examined. ANT XV/3: 48-33, numerous hydrothecae, up to 20 mm high, on O. terranovae, with developing gonothecae; 48-36, numerous hydrothecae, up to 25 mm high, on O. terranovae, with developing gonothecae; 48-50, numerous hydrothecae, up to 20 mm high, on Sc. nana, with developing gonothecae; 48-72, few hydrothecae, up to 15 mm high, on St. polarsterni; 48-210, numerous hydrothecae, up to 25 mm high, on O. terranovae, with developing gonothecae; 48-220, few hydrothecae, up to 25 mm high, on Sc. nana, with developing gonothecae; 48-276, few hydrothecae, up to 5 mm high, on Sc. nana; ANT XVII/3: 111-5, numerous hydrothecae, up to 15 mm high, on O. terranovae, with gonothecae; 111-6, numerous hydrothecae, up to 15 mm high, on Hydrodendron arboreum (Allman, 1888), O. terranovae and Sy. exochus, with gonothecae; 111-7, numerous hydrothecae, up to 15 mm high, on O. terranovae, with gonothecae; 111-9, several hydrothecae, up to 15 mm high, on O. terranovae and T. longstaffi, with gonothecae; 111-18, few hydrothecae, up to 15 mm high, on Sc. nana; 111-19, few hydrothecae, up to 20 mm high, on St. glomulosa and Tubularia sp.1; ANT XXI/2: PS65/39, few hydrothecae, up to 20 mm high, on Sc. nana and St. glomulosa, with gonothecae; PS65/166, few hydrothecae, up to 20 mm high, on A. elongatus; PS65/237, several hydrothecae, up to 15 mm high, on Sc. nana and Sy. exochus; PS65/248, few hydrothecae, up to 15 mm high, on Sy. curvatus; PS65/276, few hydrothecae, up to 25 mm high, on St. glomulosa; PS65/281, some hydrothecae, up to 15 mm high, on O. terranovae, St. nonscripta and Sy. cumberlandicus.

Remarks. According to Peña Cantero et al. (2004), C. hicksoni forms large hydrothecae (2335–2946 mm in length and 902–1417 mm in diameter at aperture). However, among the abundant material examined, some smaller hydrothecae (1000–1800 µm) have been observed. In this regard, Totton (1930), Blanco (1984) and Peña Cantero (2017) already noted a great variability in the size of the hydrotheca, but in opinion of Peña Cantero et al. (2004), Totton’s material could be composed of two different species. A detailed examination of the stolonal hydrorhiza let us confirm that some polyps with small hydrothecae (ca. 900–1000 µm) are joined through the same stolon to slightly larger ones (c. 1400–1500 µm), which in turn are united to medium-sized ones (c. 2000 µm), and so on. Furthermore, in a few occasions we observed the pioneer polyp with remnants of the planula attachment (see Fig. 7g), and thus, the first polyp of the colony, confirming the smaller size of the hydrotheca (c. 950 µm in length). Focussing on the size of the nematocysts, previous studies reported nematocysts of 17–18.5 x 4 –4.5 µm (Peña Cantero 2013), slightly larger in Peña Cantero (2014a): 19–20 x 4.5–5 µm. In present study, the size distribution of large microbasic mastigophores suggests a positive correlation between length of hydrotheca and mean size of these nematocysts (Fig. 8). We consider that the small polyps studied here (accordingly provided with small hydrothecae) also belong to C. hicksoni, based on the following reasons: in some occasions, small polyps have been noticed joined to larger ones; most small polyps were recorded on the same basibiont than larger ones, although the connection could not be ascertained; the large microbasic mastigophores of the smallest polyps always included at least a few large nematocysts, regardless of the mean size (see Fig. 8). We hypothesized that this ontogenetic drift could be attributed to changes in the trophic ecology of the species: larger polyps probably eat larger preys, and could need larger nematocysts. This is similar to previous findings relating prey size and nematocyst size, although this studies focused on various planktonic cnidarians. Purcell (1984) observed that siphonophores species with larger nematocyst capture larger prey. She subsequently suggested that the presence of longer threads in larger nematocysts could make them more effective in entangling prey. On the other hand, Carrette et al. (2002) evidenced profound changes in the ratio of different types of nematocysts between small and large specimens of the cubomedusa Chironex fleckeri Southcott, 1956 that are, in turn, correlated with ontogenetic drifts in its diet. Further research is needed regarding this finding, and specific future experimental design will shed more light on this issue.

Cnidome (in polyps within large hydrothecae) composed by large microbasic mastigophores [range 13.5–20.5 x 3.5–4.5 µm, mean 19.3±1.4 x 4.5±0.2 µm (n=56)] and small microbasic mastigohpores [range 7.5–9.0 x 1.5–2.0 µm, mean 8.2±0.4 x 1.6±0.1 µm (n=27)].

Ecology and distribution. Species previously reported at depths between 10 (Peña Cantero et al. 2004) and 779 m (Peña Cantero 2014a); material examined collected from 62 to 598 m. Species with circum-Antarctic distribution (Peña Cantero et al. 2004).