Green/Blue Masters
Also in every stage, this ship has a tendency to kidnap your ST symbol. This is often beneficial as you can win it back and have two ST's onscreen at once, side by side.
Crayfish
This is the first of the rare enemies. It shows up after stage 5.
Stingray
This one shows up a bit later.
Hawk
These faster things replace the crayfish once you get to the crazy-fast levels.
Dragonfly
The dragonfly appears in a Challenge stage.
Pinwheel
I don't know wha' this is supposed to be, but it too shows up in a Challenge level.
Federation Starship
Yeah, whatever. This one took forever to get to. I didn't expect to find any new ships, and suddenly this blatent joke appeared onscreen. I think I'll just leave it as it is.