(Figs 1 B, 2 C–D, 3 C–E)
Perigonimus belgicae Vanhöffen, 1910: 283 –284, fig. 9; Stechow, 1919: 20; Stepanjants, 1972: 58, fig. 3; 1979: 12, pl. 1 fig. 4. ‘ Perigonimus belgicae ’— Peña Cantero, 2004: 768.
Perigonimus sp. Hartlaub, 1904: 8, pl. 1 fig. 1.
Material examined. Gauss Deutschen Südpolar-Expedition 1901–1903: Syntype (ZMBCni 15702 *), 1.III. 1903, off Posadowsky Bay (Davis Sea), 2450 m, a few stems, up to 6 mm high, with gonophores, on bryozoans.
Description. Tortuous stems, up to 6 mm high, irregularly branched, with up to 11 polyps (Fig. 1 B). Stems covered almost completely with perisarc (only tips of tentacles visible) and forming distinct pseudohydrothecae, c. 280 µm in maximum diameter (Figs 2 C, 3 C–D). Perisarc typically felted; however, felt lost in most of the stems, being only present at their distal parts and on pseudohydrothecae (Fig. 1 B). Some medusa buds (c. 210 µm in diameter) present (Figs 2 D, 3 E), although in early development stage.
Remarks. According to Vanhöffen (1910) the species has no more than eight tentacles.
Unfortunately, it has not been possible to find any nematocysts and, consequently, the cnidome for this species remains unknown. In addition, despite the presence of medusa buds, their early development stage prevents me from characterizing the medusa of this species. Vanhöffen’s species is, therefore, insufficiently characterized and it is here considered a species inquirenda.
This is a very rare species, reported on three occasions, but only known for sure from the original description.
Vanhöffen (1910) considered his specimens identical with those described by Hartlaub (1904) as Perigonimus sp., although this should be confirmed by studying Hartlaub’s material. Hartlaub (1904) had previously considered his specimens related to Perigonimus cidaritis Weismann, 1883 [= Koellikerina fasciculata (Péron & Lesueur, 1810] and P. vestitus Allman, 1864 [= Leuckartiara octona (Fleming, 1823)] because of the felted perisarc envelope. Vanhöffen (1910), however, considered his species easily distinguishable from those species by its felt cover and its deep-sea habitat.
Vanhöffen (1910) already mentioned that small medusa buds were present in his material. Although in early developmental stages, the presence of medusa buds indicates that this species should be considered belonging to either Koellikerina Kramp, 1939 or Thamnostoma Haeckel, 1879 rather than to Bimeria Wright, 1859, which has fixed sporosacs. It is worth mentioning that a species of Koellikerina, K. maasi (Browne, 1910) has been reported from the Southern Ocean. Polyps of Koellikerina are only known from K. fasciculata (cf. Bouillon et al. 2006: 131) and it is noteworthy that colonies of that species have also been reported growing on spines of cidaroid sea urchins (cf. Schuchert 2007: 230), as in the case of Vanhöffen’s species.
Stepanjants (1972) reported Vanhöffen’s species from the Davis Sea. However, it should be necessary to reexamine her material to confirm it. Stepanjants’s material lacks the felt so characteristic of? K. belgicae; instead stems are covered by a dense population of ciliates. In addition, it was collected on much shallower bottoms, although eurybathic species are common in the Antarctic benthic ecosystem (Peña Cantero 2014 a). On the other hand, it agrees in the number of tentacles (about eight) and in the presence of medusa buds (in this case placed on the hydranth stems and on the hydrorhiza).
Ecology and distribution. ? Koellikerina belgicae has been found at depths between 569 m (Hartlaub 1904) and 2450 m (Vanhöffen 1910), epibiotic on spines of cidaroid sea urchins (Vanhöffen 1910) and pycnogonid legs (Hartlaub 1904). Stepanjants’ (1972, 1979) material was collected at a depth of 35 m, on Tubularia. Medusa buds were found from December to March (Stepanjants 1979).
Despite the few records of the species, it could have a circum-Antarctic distribution (Stepanjants 1979), being known from Posadowsky Bay, in the Davis Sea (Vanhöffen 1910) and at 70 ° 15 ’S, 84 °06’W, in the Bellingshausen Sea (Hartlaub 1904). As indicated above, Stepanjants’ (1972, 1979) material also comes from the Davis Sea.