Assertion: mollusk's shell | /r/CapableOf | become filled buoyant
Facets:
value: in order to support them
type: PURPOSE
Source sentences:
text: The development of a siphuncle would have allowed the shells of these early forms to become gas-filled (thus buoyant) in order to support them and keep the shells upright while the animal crawled along the floor, and separated the true cephalopods from putative ancestors such as Knightoconus, which lacked a siphuncle.