While maggot seals roam the swallow water of Silvanus global ocean, some of their relatives did first steps in the, also global, swimming forests of this planet. Different to earth athropods, these creatures have something similar to a vertebral columm, but only in the back half of their bodys. Some of this animals lost the chetin plates on their tale and use it now for more efficent swimming, and in case of some terrestrial species, climbing.
Pachytholus, one of the biggest members of this relatively new family, looks like it wouldn't be able to lift it's own body, and it would indeed collapse under it's weight... on earth. But the lower gravity of Silvanus makes this creatures surprisingly aglie.