ORIGINAL PAPER Phylogenetic relationships of the endemic Antarctic benthic hydroids (Cnidaria, Hydrozoa): what does the mitochondrial 16S rRNA tell us about it? A ´ lvaro L. Pen ˜a Cantero Æ Vicente Sentandreu Æ Amparo Latorre Received: 26 May 2009 / Accepted: 26 June 2009 / Published online: 16 July 2009 Ó Springer-Verlag 2009 Abstract Hydroidolinan hydrozoans are widely repre- sented in the benthic Antarctic ecosystem, mainly by some endemic and putative monophyletic groups, never included in molecular phylogenetic analyses. 38 partial sequences of the mitochondrial 16S rRNA gene were obtained for 38 species belonging to 14 families (six anthoathecates and eight leptothecates) and 20 genera (7 anthoathecates and 13 leptothecates). These sequences were combined with 108 additional sequences retrieved from the GenBank to investigate both the hypothetical monophyletism and the phylogenetic relationships of those endemic Antarctic groups; the potential use of the marker for barcoding was also investigated. Our results uphold the monophyly of some important hydroidolinan groups, such as the super- family Plumularioidea (together with all its families, including Schizotrichidae, fam. nov.) and the Aplanulata. Concerning the Antarctic endemic groups, most results as monophyletic (Oswaldella, Schizotricha and Staurotheca), some genera form part of the expectable groups (e.g. Abietinella, located into the monophyletic Zygophylacinae clade) and, finally, others have shown a surprising position (e.g. Stegella, closely related to Lafoeinae, or Billardia and Stegopoma, allied with Hebellidae). Finally, our study has shown the utility of the marker to recognize the Antarctic species considered, but the low genetic divergence in some of the most important Antarctic groups suggests being careful when using it for DNA barcoding in the case of the original Antarctic hydroid fauna. Keywords Southern Ocean Á Benthos Á New family Á Phylogeny Á Monophyly Introduction Of the world ecosystems, the marine Antarctic benthic system is one of the most important and interesting from the scientific point of view. It includes some of the highest productive habitats of the planet, but it is also characterized by extremely high levels of endemism; for example, [ 90% in Pycnogonida (Fry 1964) and 95% in Amphiphoda (Jazdzewski et al. 1991) or fishes (Andriashev 1964). Hydrozoans constitute an omnipresent zoological group in the benthic Antarctic ecosystem (Clark and Johnston 2003). Furthermore, they have some intriguing features relating to their origin and evolution, such as the relatively low diversity at the genus level, the high level of endemism at the species level (ca. 70%) and a diversity restricted to a few, presumably monophyletic groups (Pen ˜a Cantero and Garcı ´a Carrascosa 1999). In recent years, the studies that carried out have con- tributed enormously to the scientific knowledge of the biodiversity of the group, increasing spectacularly the number of known species (e.g. Pen ˜a Cantero and Garcı ´a Carrascosa 1995; Pen ˜a Cantero et al. 1996, 1997a, b, c, 1999, 2002; Pen ˜a Cantero and Vervoort 2003, 2004, 2005), but also to the knowledge of the biology, ecology and A ´ . L. Pen ˜a Cantero (&) Instituto Cavanilles de Biodiversidad y Biologı ´a Evolutiva, Universidad de Valencia, Fundacio ´n General Universidad de Valencia, Apdo. Correos 22085, 46071 Valencia, Spain e-mail: alvaro.l.pena@uv.es V. Sentandreu Á A. Latorre Instituto Cavanilles de Biodiversidad y Biologı ´a Evolutiva, Universidad de Valencia, Apdo. Correos 22085, 46071 Valencia, Spain e-mail: vicente.Sentandreu@uv.es A. Latorre e-mail: amparo.latorre@uv.es 123 Polar Biol (2010) 33:41–57 DOI 10.1007/s00300-009-0683-5