The beastworm has evolved from the stumpworm. It has nearly tripled in size, and in doing so has made a few necessary adaptations. The smell receptors, which had been exclusively inside the mouth, have started moving to the outside. This means they do not have to have their mouth open all the time to smell. Their sense of smell has also heightened. They will now eat both living and dead animals, though they will only eat carrion if there is no other food available. Because of their size, the old way of molting is no longer efficient. Instead, its skin and exoskeleton shed continuously, in much smaller pieces. This means that the shell is no longer as nearly as rigid as it used to be.
To compensate for its lack of support, the beastworm has developed an internal support structure made of the same material the old, very hard shells were. Its increase in size also means that the old way of absorbing oxygen directly through the skin no longer worked well enough. Instead, the beastworm has evolved numerous, tiny "microlungs," located all over its skin, which allow it to breathe much more effectively. Its previously stumpy legs have evolved so that they can support the weight of the worm, allowing it to walk slowly (though still faster than its old "wiggling") over the ground, with its tail dragging behind it. Although it can no longer fit into the airhole of plents, it still eats them. Instead of plugging their airholes with their bodies, they simply bite down over the airhole as hard as they can and don't let go. They still attack by jumping. They have also developed an internal "force" sensor that allows them to feel vibrations.
Artwork by OviraptorFan