Benthic hydroids (Cnidaria, Hydrozoa) from the Weddell Sea (Antarctica) Author Soto, Joan J. Author Peña, Álvaro L. text Zootaxa 2019 2019-03-22 4570 1 1 78 journal article 27992 10.11646/zootaxa.4570.1.1 66601a1e-ba16-41b2-b182-0fd80e75ccba 1175-5326 2608527 EF369E98-EBD9-4647-B081-65AD1794A27C Billardia subrufa ( Jäderholm, 1904 ) ( Fig. 7 k–m) Material examined. ANT XV/3 : 48-4 , one colony, c. 50 mm high; 48-5 , some stems, up to 50 mm high, on Sc. unifurcata , S. lobata and sponge, with gonothecae; 48-27 , one colony, c. 40 mm high, and some stems, up to 5 mm high, on E. generale ; 48-44 , some stems, up to 60 mm high, on S. lobata and polychaete tube, with gonothecae; 48- 63 , one colony, c. 10 mm high; 48-70 , one colony, c. 90 mm high, with gonothecae; 48-72 , several stems, up to 30 mm high, on sponge, with gonothecae; 48-77 , one colony, c. 45 mm high; 48-82 , one colony, c. 110 mm high, with developing gonothecae and few stems, up to 20 mm high, on St. polarsterni ; 48-154 , one colony, c. 60 mm high; 48-168 , one colony, c. 130 mm high, with gonothecae; 48-194 , one colony, c. 50 mm high; 48-197 , several stems, up to 90 mm high, on dead octocoral, with gonothecae, and some stems, up to 11 mm high, on Eudendrium sp.1; 48-222 , one colony, c. 150 mm high; 48-276 , one colony, c. 190 mm high, with gonothecae, on Sc. nana ; 48-297 , several stems, up to 45 mm high, on ascidian, with gonothecae; ANT XVII/3 : 111-5 , some stems, up to 13 mm high, on O. terranovae ; 111-6 , one colony, c. 55 mm high, with gonothecae; 111-9 , few stems, up to 35 mm high, on O. terranovae and S. lobata ; 111-18 , one colony, c. 65 mm high, with gonothecae, and numerous stems, up to 30 mm high, on O. terranovae , Sc. nana and polychaete tube, with gonothecae; ANT XXI/2 : PS65/39 , one colony, c. 20 mm high; PS65/121 , one colony, c. 30 mm high, and few stems, up to 10 mm high, on Sc. nana ; PS65/132 , one colony, c. 82 mm high, on bryozoan, with gonothecae; PS65/148 , few stems, up to 8 mm high, on O. erratum ; PS65/166 , one colony, c. 110 mm high, with gonothecae; PS65/174 , one colony, c. 90 mm high, on O. erratum , with gonothecae, and few stems, up to 90 mm high, with developing gonothecae; PS65/175 , numerous stems, up to 110 mm high, on O. erratum , octocoral, bryozoan and polychaete tube, with gonothecae; PS65/237 , several stems, up to 60 mm high, on Sc. nana , S. lobata and sponge, with gonothecae; PS65/245 , one colony, c. 50 mm high; PS65/253 , one colony, c. 40 mm high; PS65/259 , one colony, c. 75 mm high; PS65/265 , one colony, c. 120 mm high, with gonothecae, and few stems, up to 15 mm high, on St. polarsterni ; PS65/274 , few stems, up to 12 mm high, on Sc. unifurcata and St. polarsterni ; PS65/276 , few stems, up to 6 mm high, on S. lobata ; PS65/278 , one colony, c. 60 mm high, and few stems, up to 10 mm high, on sponge; PS65/279 , one colony, c. 60 mm ; PS65/280 , one colony, c. 20 mm high; PS65/281 , one colony, c. 140 mm high, on gravel and sponge, with gonothecae, and some stems, up to 25 mm high, on O. terranovae ; PS65/336 , few stems, up to 10 mm high, on Sc. nana . Remarks. Similarly to the process described for S. lobata , several specimens have been observed using a wide range of basibionts as substrate (octocorals, hydroids or polychaete tubes, among others). Large colonies are seen in many cases growing on its basibiont until overgrowing entirely the host colony, which is completely indiscernible unless a cross section is done. We suggest that B. subrufa might behave as an aggressive epibiont species that uses a basibiont to reach large sizes, as it is known from the zoantharian Savalia savaglia ( Bertoloni, 1819 ) ( Zibrowius 1985 ) . As mentioned above, the relationship can be categorized as parasitism sensu lato , in which the epibiont is detrimental to the host but is not metabolically dependent upon it (see Gili et al. 2006 and references therein). That assumption implies that B. subrufa should have a quicker growth rate than its host. The presence of horizontal growing by polysiphonic stems could enhance its colonizing efficiency. Further in vivo experiments are needed to test this hypothesis. Ecology and distribution. Species collected at depths between 25 ( Stepanjants 1972 ) and 1030 m (Peña Cantero et al. 2004); present material from 62–583 m depth. Antarctic-Patagonian species (Peña Cantero et al. 2004).