The Participants panel includes everyone who joined the meeting, plus the GMSO Audio Assistant. The assistant works in the background and links the meeting audio for your dial-in participants with the Skype audio participants in the meeting. Do not dismiss the Audio Assistant.
Presenters v attendees
Unless you set the presenter option when scheduling the meeting, everyone who joins via Skype client or web app enters the meeting with the presenter role. Dial in audio connections are listed under Attendees.
Presenters can mute the audience and manage other participants. As the host, you might want to demote presenters to attendees. At the bottom of the Participants panel, click Participant Actions, and then click Everyone an Attendee.