I was reading my fish book last night and I reached this ocean sunfish, also known as a mola mola. I thought it was a little strange that they drew the fish, like, turning right, but it turns out the fish just... ends? It literally doesn't have a tail part. That's the end of the fish.
This is a different species in the genus, but it's shaped the same, just a fish head with a big-ass dorsal and anal fins. I think it's kind of cute in a way. Because it doesn't have a tail, it "swings its dorsal fin and anal fin in a characteristic sculling motion", which seems to mean waving both fins in the same direction back and forth.
But these photos with the fish alone don't really give a sense of the scale of these fish, and as it turns out, these fish are HUGE! A fin alone is nearly the size of a human!
The Monterey Bay Aquarium has mola mola in captivity, surprisingly, although they don't seem to be on display. It's astonishing they can healthily keep a fish this large (that isn't, like, a shark).
Here's a neat video of a mola mola swimming around, and then stopping by some smaller fish to get the parasites on its skin cleaned off: