The Dark Coronatus is a Seahorse. He only appears in Darius Twin.
Dark Coronatus cycles between three attacks, a common enough phenomenon. The part of him you should aim for is the middle of his body, while avoiding three things. His three energy ball-arc from his head or so. The birthed little coronati from his midsection. This is quite biolgically accurate, and tells you that Dark Coronatus was built as a male seahorse. He stretches himself out and fires a four-bullet arc.