Gnathostomes
Suction phase: Buccal cavity and opercular cavity work in a synchronous pattern to drive water in a nearly continuous unidirectional flow across gill curtain.
buccal cavity expands, oral valves open & water rushes in, across gill curtain into opercular cavity
Force Phase: oral valves close & opercular valves open. Both buccal and opercular cavity compress forcing water from buccal cavity across gill curtain out opercular valv