Sanitized Octarians were either infected by some aqua green substance or are created by it, maybe even a combination of both. Tentacle based ones tend to disappear in a glitch-like fashion after being splatted, meaning they are not naturally cut tentacles, as for the Octolings, they were Sanitized the same way Agent 3 got slightly Sanitized near the surface. So either way, I theorize that the aqua green substance are actually cells from the blended test subjects that are somehow kept alive, which could be how Tartar is able to create the tentacle Octarians.