Apothecary
An Apothecary is a Space Marine specialist, equivalent to a Medic. The senior Apothecary is known as the Master of the Apothecarion (the fortress-monastery's medical center) or Chief Apothecary. Armed with standard Space Marine gear and a Narthecium.
Since Space Marines have undergone genetic augmentations to survive nearly anything, an Apothecary's real battlefield roles involve three jobs: stabilizing, mercy killing and extracting. While Space Marines can endure damn near anything except the most serious injuries, Apothecaries frequently need to stabilize them long enough for their gene-seed to start up and heal them. If a Marine has been too badly injured to be saved, then the Apothecary applies "the Emperor's Peace", a mercy kill by driving a Reductor (a sharpened needle) into the Marine's skull to quickly end his pain. If a Marine has died, it is the Apothecary's duty to extract the progenoids from his dead brother. Off the battlefield, they also implant Space Marine Initiates with the extracted progenoids, and make sure they and full battle-brothers are healthy or to check for unhealthy mutations.
Sanguinary Priest
The Blood Angels are a little weird, so they call their Apothecaries "Sanguinary Priests." There's a lot of weird blood rituals they do.
Also, they LITERALLY carry the blood of Sanguinius, since they're injected with a sample of it when they become Sanguinary Priests. This means they are the prettiest Marines, as they look the most like Sanguinius.