Vogel
Every bunch of Vogels is led by one leading Vogel. When eliminating the leader, each Vogel will re-arrange to change their formation. Now, it's easier to blast-off a complete line of enemies at the same time.
Walker
This walker is walking on the ground and shoots aimed bullets at you.
Galama
Galama swims through the cave and drops some exploding bullets from its back. It's recommend to put the pod on the backside when encountering this enemy.
Dreher
Dreher flies around and is pretty quick. When turning a complete circle ths enemy gets pretty dangerous.
Vogel appears in Stage 4, Walker in Stage 1, Galamar in Stage 2 and Dreher in Stage 3.
Source: DUX blog