The Heat Arrow is a Ocean sunfish. It only appears in Super Darius II game.
Heat Arrow is a good spiritual predecessor of the Darius II end bosses, in that (a) he uses two attacks but makes them count, and (b) he turns from side to side a lot. So, on to (a). He first fires a little blue ball that bursts into a (wide) six-bullet arc in your general direction. Nothing as vicious as Fatty Glutton's arc, I must say. Then, his dorsal and ventral fins bend back and the front of him opens out to reveal a BIG cannon which, predictable enough, fires BIG bolts at you. Intimidating but not terribly dangerous.
The tricky thing is when, after finishing this two-attack cycle, he starts to turn and, being a big bastard, can easily squash you while moving across the screen. See above to see what I mean . Blowing off the fins can help, but not much, to free up space. However, he doesn't move arcoss the screen to fast, so there's no fear of a cheap ramming attack. Lastly, after enough damage his laser shots get replaced by this huge beam from its mouth.