I hope no one minds, but I'm convinced that there are a few species of pretty large worms on Mars. One kind opens at one end, and the worm comes out of that... sometimes it's ends can open a few times. I will draw my concept to you soon... When first coming out, the opening has a zig-zag pattern... sometimes the zig-zag pattern is more angular and sometimes its less angular... there are "tube worms" here on Earth... personally I feel that some species of Mars worms are what makes those transparent tubes seen from the MOC satellite images. They are worm holes. Even Earth worms use secretions to tunnel through the dirt to keep their small tunnels open. Perhaps the Mars worms do the same thing, only on a larger scale?
Here are two "hidden" images of one type of a Mars worm... It shows the one worm coming out of that typical "zig-zag" opening. A bit hard to make out due to tampering but still identifiable.