Leech

A very pretty photo....

I was bitten by one of these in Sabah, Malaysia. This is a hungry one. If it was fatter and well-fed, you'd see that they're commonly called "tiger leeches" because of their lengthwise darker and lighter stripes. Most people feel a stinging or pinching sensation when tiger leeches bite (unlike most leeches, whose venom contains an anesthetic), so they usually get brushed off quickly. I'm the one in a million who is immune to the venom, so the tiger leech under my arm had a chance to get nice and fat before I discovered it!

Looks like a type of Leech.