Some species do not use transporter technology for a variety of reasons. In the first appearance of Trill in the "TNG" episode "", Trill were unable to be transported, once joined with a symbiont. It seems that was due to the symbiont being detected and removed by the transporter technology as an infestation in the host. Odan, the Trill host in this episode, is reluctant to say why he will not travel this way, and it only becomes apparent that he is carrying a symbiont when he is later injured. All the crew of the "Enterprise" react as if they have had no contact with this species before. It later becomes apparent that joined Trill have been working in the Federation for some time.