A Yammosk keeper was a title held by certain Yuuzhan Vong.
The keeper was a custodian who tended to the needs of a yammosk war coordinator. Their duties allowed them to telepathically connect to the powerful beasts and ensure that a commander's task was done.
The Priest Harrar had a Yammosk keeper on his personal vessel which contained a war coordinator. He confirmed with the keeper on whether the yammosk had accepted the Trickster's dovin basals in its communication family.