The Clown Triggerfish, Balistoides conspicillum, is solitary, aggressive, and territorial. When its first dorsal spine is upright (as drawn here), it is locked in place by the second spine. The first spine can only be lowered after the second is pulled back, like a trigger.
Clown Triggerfish feed on meaty foods such as clams, shrimp, or smaller fish. In aquariums, they can become tame enough to be hand-fed. But watch out for those sharp teeth!
Sea hares, as you know, eat algae… unless they’re starving in captivity, in which case they may try to eat each other! But that’s a story for another time.