A single tunicates has 2 openings, however, they can be solitary or colonial. Sometimes in the colony, each individual has a siphon all to themselves and then also shares a common siphon with the rest of the crew. There can be tissue over the colony to cover of their individuality, so that they look like a single blob with multiple siphons. In a sponge all those siphones belong to the single animal. In a tunicate, the siphons all belong to multiple individuals under a single cape.
Sea squirts got their name from their very forceful ability to squirt water and retract. Some sponges can sneeze, or clear their filter system if clogged, but it's not the same swift motion.