Zanclea hicksoni ( Stepanjants, 1972 )

Soto, Joan J. & Peña, Álvaro L., 2019, Benthic hydroids (Cnidaria, Hydrozoa) from the Weddell Sea (Antarctica), Zootaxa 4570 (1), pp. 1-78 : 20

Zanclea hicksoni ( Stepanjants, 1972)

( Fig. 4 j–o)

Material examined. ANT XV/3: 48-31, a single polyp, c. 3 mm high, on O. terranovae ; ANT XVII/3: 111-9, numerous polyps, up to 5 mm high, on T. longstaffi and E. generale .

Remarks. According to Peña Cantero et al. (2013), Z. hicksoni is conspecific with Corynidae Species B Hickson & Gravely, 1907. The species was later described as Gemmaria hicksoni Stepanjants, 1972 . As previously noted by Hickson & Gravely (1907), polyps examined here are provided with hydrorhizal filaments which anchor them to the substrate ( Fig. 4l ). Additionally, we have observed some large specimens with linear clusters of 3–5 tentacles, being the central one larger ( Fig. 4n ). These two characteristics are diagnostic features of the genus Monocoryne Broch, 1910 (Fam. Candelabridae Stechow, 1921 ) according to Stepanjants et al. (2003). Conversely, there are no Zanclea species with those characters (cf. Bouillon et al. 2006). According to Stepanjants et al. (2003), the tentacles of Monocoryne sp. Stepanjants, 1979 are irregularly distributed, and can be either solitary or arranged in groups of three, being one larger ( Stepanjants et al. 2003: 104). Among the several polyps observed, some certainly resemble a zancleid ( Fig. 4k ), while the largest ones have more affinities with Monocoryne ( Fig. 4 n–o). Early-developing polyps are also present among the material examined ( Fig. 4j ). The great morphological variability observed here, the very few available polyps examined by previous authors, and the lack of mediumsized specimens could be the reason why Stepanjants (1979) described two different species (i.e. Gemmaria hicksoni and Monocoryne sp.). Finally, the type and size of the nematocysts of Z. hicksoni obtained by Peña Cantero et al. (2013), of Monocoryne sp. by Stepanjants et al. (2003), and of the present material are almost identical. Therefore, Z. hicksoni might be conspecific with Monocoryne sp. described by Stepanjants (1979) and Stepanjants et al. (2003), with subsequent family and genus re-allocation. However, due to the reproductive structures of Z. hicksoni are still unknown, further evidence is needed to confirm its true identity.

Cnidome composed by small stenoteles [range 8.5–11.0 x 6.5–8.0 µm, mean 9.6±0.8 x 7.1±0.4 µm (n=15)], large stenoteles [range 13.0–17.0 x 11.0–14.0 µm, mean 14.9±1.0 x 12.7±0.7 µm (n=15)], haplonemes (isorhiza) [range 14.0–18.0 x 4.5–7.0 µm, mean 16.7±1.4 x 5.7±0.7 µm (n=14)] and desmonemes [range 5.0–8.5 x 4.5–5.5 µm, mean 6.9±0.8 x 5.1±0.3 µm (n=17)].

Ecology and distribution. Previously found at depths from 12 (Peña Cantero et al. 2013) to 183 m ( Hickson & Gravely 1907, as Corynidae Species B); present material was collected at 62– 64 m. All previous records were restricted to East Antarctica (see Peña Cantero et al. 2013); present study confirms its occurrence in West Antarctica and constitutes the first record from the Weddell Sea, pointing to a circum-Antarctic distribution.

Figures

FIGURE 4. a–i Tubularia longstaffi: a polyp-carrying tube; b male polyp; c blastostyle with developing male gonophores; d blastostyle with fully-grown male gonophores; e female polyp; f blastostyle with fully-grown female gonophores; g–h detail of female gonophores carrying actinulae; i actinulae in different stages of development. j–o Zanclea hicksoni: j early-developing polyp, k expanded young polyps, l expanded polyps with hydrorhizal filaments, m contracted polyp, n–o detail of polyps showing tentacle arrangement in linear clusters (arrows).