Does the manual call it that ?
This is more or less a typical water pump other than some are plastic
On a mercury the black thing is the seal holder and it slips right out as its rubber
Your kind of digging into gearbox now and need to proceed with a bit more guidance from a manual as part #17 is holding some important stuff in place
so it is easy to get in trouble about right now
For example on a Gen II lower you pull the shift shaft right out BUT IF you do it on a GEN I (older style) you have to tear down the entire lower-unit to fix that mistake