Just finished reading an older manga and enjoyed it a lot. I love the 1980's style to it.
http://www.onemanga.com/Parasyte/
Parasyte isn't just about regular old parasites - as the unusual spelling the title of the manga indicates -- but about creepy sentient alien parasites that take over the human body. The narrative of this title actually focuses on an alien-body-snatch-gone-wrong, as our protagonist, Shinichi, manages to stop the progress of his parasite before it reaches his brain. Unfortunately, now he's got to share his body - specifically his left arm as the image above hints at -- with this invader and learn to share one vessel with two beings with conflicting values, needs, and desires. The wonder of this title is how well it envisions this strange new life for Shinichi and his new companion (called "Migi") and the dangers that come with this new existence - many of those dangers coming from more successful alien parasites which wear their victims' faces and tend to wreak havoc, with occasionally eating human beings and all.