Review of some little-known benthic hydroids (Cnidaria, Hydrozoa) from the Southern Ocean Author Peña Cantero, Álvaro L. text Zootaxa 2015 3972 3 369 392 journal article 10.11646/zootaxa.3972.3.4 37cf6488-091a-40ce-ae0a-2e251f6254ea 1175-5326 236731 C1698260-269E-4D15-A562-D8FF46751F7F Perarella clavata ( Jäderholm, 1905 ) ( Fig. 6 A–C) Hydractinia clavata Jäderholm, 1905 : 5 –6, pl. 3 figs 6–8; Stepanjants, 1979 : 15 , pl. 1 fig. 9; Blanco, 1994a : 152 ; 1994b: 184; Peña Cantero, 2004 : 768 ; Stampar et al ., 2006 : 58 . Stylactella clavata — Stechow, 1925 : 401 ; Iwasa, 1934 : 262 , 269. Cytaeis clavata — Bouillon et al ., 2006 : 145 . Perarella clavata — Rees, 1962 : 394 , fig. 11; Peña Cantero, 2008 : 453 . Material examined. Antarctic Swedish South Polar Expedition. 1901-03 : Type (SMNH—7946), Stn 8, 11.II.1902 , 64°03’S , 56°37’W (Erebus and Terror Gulf, Graham Region), 360 m , soft clay, colony with numerous polyps and gonophores, on gastropod shell. Description. Stolonal colony growing on gastropod shell. Hydrorhiza consisting of a mesh of anastomosing tubes of perisarc, not covered by a coenosarc layer. With gastrozooids and gonophores. Neither spines nor dactylozooids. Gastrozooids relatively large ( Fig. 6 A) [ 6–8 mm long and 0.3 to 1 mm wide, according to Jäderholm (1905) ], with conical hypostome and a distal crown of 15–17 filiform tentacles ( Fig. 6 A, B). Gonozooids absent; gonophores directly arising from hydrorhiza, club-shaped ( Fig. 6 C), about 2 mm long and 0.50–0.75 mm wide. Both gastrozooids and gonophores with a short, basal cup of perisarc ( Fig. 6 A, C). Female gonophores with a very large number of eggs. Measurements (in µm). Cnidome : microbasic mastigophore [range 8.0–9.5 x 3.5–4.5, mean 9.2±0.5 x 4.2±0.3 (n=10); ratio, range 2.0–2.4, mean 2.2±0.1 (n=10)], desmonemes [range 5.5–6.5 x 3.5–4.5, mean 6.1±0.3 x 4.2±0.3 (n=10); ratio, range 1.3–1.6, mean 1.5±0.1 (n=10)]. FIGURE 6. Perarella clavata (Jäderholm, 1905) : A, polyp showing basal cup of perisarc (arrow); B, distal part of polyp; C, female gonophore showing basal cup of perisarc (arrow). Scale bar: 500 µm (A–C). Remarks. Rees (1962: 394–395, fig. 11) also provided a description of the species after examining the type material. Perarella clavata is a morphologically well-characterized species, with gonophores arising directly from the hydrorhiza. The only missing relevant information concerned the cnidome. I have tried to fill this gap with the reevaluation of the type material. The presence of a basal perisarc cup also supports that this species belong to the family Cytaeidae . Rees (1956 , 1962 ) re-established the genus Perarella for species with fixed sporosacs or degenerated medusae. Bouillon et al . (2004 , 2006 ), following the idea that genera should not be delimited based exclusively on medusa reduction, considered, however, this genus congeneric with Cytaeis . Nevertheless, Schuchert (2007) indicated that this approach is valid in cases where a hydroid can be attributed unambiguously to a certain family, but not in the case of Perarella , which could even belong to the families Bougainvilliidae or Pandeidae . He concluded that it is advisable to retain the genus Perarella until its affinities are clearly revealed by molecular phylogenetic analyses. I agree with his opinion. Ecology and distribution. Perarella clavata has been collected at depths from 220 m ( Peña Cantero 2008 ) to 360 m ( Jäderholm 1905 ), epibiotic on gastropod shells ( Aforia magnifica ) ( Jäderholm 1905 ; Peña Cantero 2008 ). It has been found with gonophores in January ( Peña Cantero 2008 ) and February ( Jäderholm 1905 ). Perarella clavata is endemic to West Antarctica , being only known from the Erebus and Terror Gulf, Graham Land ( Jäderholm 1905 ) and off the south of Livingston Island , in the South Shetland Islands ( Peña Cantero 2008 ).