I figured it out. Someone else probably has already, but I assure you that I didn't get this from anywhere else.

Take a look at Tilius's scan of Pridak. Notice how the squid in the launcher is slightly shorter than the one clipped to his armor. This observation has led me to this conlusion:



See? To fit the polyp into the launcher, the tail has to scrunch up. When you press the knobs on the sides of the launcher, the clip holding the polyp from springing out opens and releases it, much like the Lego blunt shooters.