http://en.memory-alpha.org/wiki/Norvo_Tigan<br/><div class="quoteheader"><div class="topslice_quote">Quote</div></div><blockquote class="bbc_standard_quote">Norvo Tigan was the younger brother of Ezri Tigan and Janel Tigan, and the son of Yanas Tigan. </blockquote><div class="quotefooter"><div class="botslice_quote"></div></div><br/>The page contains spoilers to the show, but we can establish precedent for surnames for Trill.  It looks like they abandon their old last names when they get joined.