On a few benthic hydroids (Cnidaria, Hydrozoa) from the Kerguelen Islands (southern Indian Ocean), including the description of a new species Author Peña Cantero, Álvaro L. 0000-0003-3056-6673 Instituto Cavanilles de Biodiversidad y Biología Evolutiva / Departamento de Zoología, Universidad de Valencia, Valencia, Spain, Apdo. Correos 22085, 46071 Valencia, Spain. alvaro.l.pena@uv.es text Zootaxa 2022 2022-07-14 5165 2 274 286 journal article 10.11646/zootaxa.5165.2.7 0b3e63f8-e436-4933-8175-1fc0e46bffe1 1175-5326 6831887 87810F4C-9824-4EBB-AE58-1CCFD65FDEE3 Candelabrum bitentaculatum sp. nov. ( Figs 1–2 ) Material examined. Holotype : PROTEKER 2: Baie Philippe , one polyp 108 mm long, with gonophores ( MNHN IK – 2012–10431 ). Description . Hydranth about 108 mm long, with an 8 mm-long basal part, a gonophore-bearing middle part, about 40 mm long, and a 60 mm-long distal part provided with hundreds of capitate tentacles ( Fig. 1A ). Mature blastostyles unbranched, short, with up to six distal capitate tentacles and up to three basal, spherical gonophores in close proximity ( Fig. 1B–E ). The most basal gonophore barely developed, the others mature ( Fig. 1D ). Number of tentacles on blastostyles without gonophores ranging from a single distal tentacle to six ( Fig. 1B– E ). A few gonophores, the most distal ones, arising directly from the polyp’s body wall between normal tentacles ( Fig. 1F ). Hydranth basal part with blastostyle-like structures with four distal capitate tentacles, but also with five sucker tentacles below, forming a sort of crown ( Fig. 1G–H ). Some of the sucker tentacles with a small piece of perisarc ( Fig. 1H ). Cnidome ( Fig. 2 ) consisting of microbasic euryteles [22.6±1.1 x 8.9±0.5 µm (n= 10), range 21–24 x 8–10 µm],?mastigophores [20.1±0.9 x 6.3±0.3 µm (n= 10), range 19–21.5 x 6–6.5 µm], larger desmonemes [13.1±0.2 x 10.1±0.2 µm (n= 10), range 13 x 10–10.5 µm], smaller desmonemes [9.3±0.4 x 6.4±0.3 µm (n= 10), range 9–10 x 6–7 µm] and stenoteles [11±0.0 x 9±0.0 µm (n= 10), range 11 x 9 µm]. Remarks. Although the area below the gonophore-bearing blastostyles extends over the basal eight millimetres, the blastostyle-like structures described above, provided with both capitate and sucker tentacles, only extent over the most basal five millimetres. If the presence of these sucker tentacles defined the basal part of the polyp, it then would be shorter, only five millimetres long. The isolated gonophores arising directly from the hydranth body wall between tentacles ( Fig. 1F ), above the blastostyle area, might represent male gonophores. If this were the case, the species would be monoecious. Candelabrum bitentaculatum sp. nov. differs from all known species of the genus by the unique blastostyle-like structure of the basal part of the polyp. From the southern hemisphere Candelabrum species, Candelabrum bitentaculatum sp. nov. also differs in several important features, mainly concerning the gonophore-bearing blastostyles. By having unbranched blastostyles, the present species differs from Candelabrum harrisoni ( Briggs, 1928 ) , whose blastostyles have an irregularly lobed base, from Candelabrum penola ( Manton, 1940 ) , which has irregularly lobed or branched blastostyles, and from Candelabrum meridianum ( Briggs, 1938 ) , whose blastostyles are branched. In the arrangement of the blastostyles, which have no defined pattern, Candelabrum bitentaculatum sp. nov. differs from Candelabrum capensis ( Manton, 1940 ) and C. tentaculatum ( Millard, 1966 ) , in which the blastostyles are arranged in a single whorl. In the number of gonophores per blastostyle, Candelabrum bitentaculatum sp. nov. also differs from most species. As indicated above, there are only three gonophores, the most basal one barely developed. By contrast, in the species considered, the number of gonophores is higher. Thus, Candelabrum australe ( Briggs, 1928 ) has three to four mature and six to eight immature gonophores, C. penola has up to 10 gonophores, C. capensis nine and C. tentaculatum and Candelabrum valdiviensis Galea & Schories, 2014 up to eight. Even Candelabrum austrogeorgiae ( Jäderholm, 1904 ) , whose blastostyles usually have one to three gonophores, has been observed with up to six gonophores per blastostyle. FIGURE 1. Candelabrum bitentaculatum sp. nov. : A, hydranth; B, basal and middle part of polyp; C, general view of polyp’s gonophore-bearing middle part; D, blastostyles with gonophores; E, blastostyles; F, general view of a portion of polyp’s distal part showing the location of putative male gonophore (arrow), with close-up showing that gonophore; G, general view of basal part of polyp; H, basal part of hydranth showing blastostyle-like structures (arrow pointing to one of them clearly showing the capitate and sucker tentacles), close-up showing sucker tentacles with perisarc plate. Scale bar: 10 mm (A, B), 5 mm (D). FIGURE 2. Candelabrum bitentaculatum sp. nov. : A, discharged microbasic eurytele; B, undischarged microbasic eurytele (arrow); C, larger and smaller desmonemes and?mastigophore (arrow); D, larger and smaller desmonemes; E, discharged desmoneme; F, stenotele. Scale bar: 10 µm. In the number of tentacles on the blastostyles, Candelabrum bitentaculatum sp. nov. , which has up to six distal tentacles, differs from C. meridianum , which has none, and C. harrisoni , which has only one distal tentacle. Candelabrum austrogeorgiae has either a single stout, elongated tentacle at the tip, or a few smaller, weakly developed ones. On the other end, C. tentaculatum has about 25 tentacles. By its naked basal part, Candelabrum bitentaculatum sp. nov. also differs from C. harrisoni , in which the basal part is covered with perisarc. Vanhöffen (1910) reported Candelabrum austrogeorgiae (as Myriothela Austro-georgiae ) from Kerguelen, indicating that his material coincided completely with the upper part of the specimen depicted by Jäderholm (1905 , pl. 2, fig. 1). However, Vanhöffen’s material consisted of a 10-mm-long fragment corresponding to the most distal part of a polyp, with about 40 rows of densely packed, capitate tentacles. In the light of the present results, it is plausible to consider that Vanhöffen’s material could actually belong to Candelabrum bitentaculatum sp. nov. , which also has a distal part provided with hundreds of capitate tentacles. Ecology and distribution. Candelabrum bitentaculatum sp. nov. was collected at a depth of 102 m in Philippe Bay; gonophores in November. Etymology. The specific name bitentaculatum refers to the presence of two types of tentacles, capitate and sucker-tentacles, in the blastostyle-like structures of the hydranth basal part.