30 teams in NHL, 28 teams in AHL?

I’ve always thought that the AHL was the top minor league attached to the NHL, and that each NHL team had an AHL affiliate. But today I was reading the new World Cup of Hockey media guide and I saw a reference to there being 30 NHL teams but only 28 AHL teams. What’s up with that? Who doesn’t have an affiliated AHL team? Do some teams share?

Carolina Hurricanes and Calgary Flames share the Lowell Lock Monsters.

Minnesota Wild and Dallas Stars share the Houston Aeros.

From this site.