What is a mysqld process in a MySQL cluster?

Question

As I know, a mysqld process is a kind of a router of a MySQl cluster. It directs requests to the right ndbd node.

Assuming I have 3 ndbd nodes on 3 different machines and I don't use replication. How many mysqld proccesses do I need? I would say one? For me its like a master-slave architecture (comparable with mongodb) But I saw configurations where each ndbd node also has one mysqld proccess. Why?