huh? They look like giant worms, are super-fast and extremely tough to kill. They attack even other Shadowspawn.

What we don't know if how they were in the WOS, when they transformed from this "wormish" state to full-grown Jumara (and Sammael hinted they can't transform anymore for some unknown reason.. but that opinion might be more reliable if it had come from Aginor instead of Sammael. I've not given up on the possibility the Worms can transform once Shai'tan's powers have grown enough - when the Seals are gone for instance). It's Jumara we have no idea what they were like, or what they could do. The only hint we have is that the name of this monster either became the name of the harshest month of winter in the third Age, or Aginor had named them after the harshest month of winter in the AOL too,