DNA extraction, amplification and sequencing
DNA of A. hemprichi, H. periglandulata and S. subterranea was extracted according to a standard Chelex™ procedure (Singer-Sam et al., 1989; Hillis et al., 1996). DNA extraction of P. heideri and A. marina was made using “High Pure PCR Template Preparation” from Boehringer-Mannheim Biochemicals, and that of Ctenodrilidae n. gen et sp. and P. purpureus using “QIAamp DNA Mini Kit” from Quiagen, following the instructions of the manufacturers. 18S rRNA gene fragments of A. hemprichi and H. periglandulata were amplified and sequenced according to Martin (2001), using the 16 primers of Winnepenninckx et al. (1994), kindly granted us by the authors. Specimens of the other taxa were analysed following the protocol described in Erséus et al. (2000).