I am pretty sure now that Riley didn't attack his own tail and that it did get sucked into the funny little gap in my filter when the two halves click together. It has been blocked up with a tiny piece of cut sponge and his tail hasn't been caught again.
Riley's tail still looks ragged, compared to how it was originally, but it looks a bit less ragged than the picture above. He has had the most minute bit of regrowth where it got broken off. Actually, he seems to have had more growth on the very bottom of his tail where nothing had been ripped. At first, as I've been watching him like a hawk, I feared it was the beginning of fin rot since it was such a light color... but no, he is just growing more bottom fin. I hope the ragged bit catches up... I really like his smooth tail edges that he had before this accident.
I've also bought Indian Almond leaves and I have had a leaf floating in his tank. The water doesn't look as tea light as I expected... it is more like the light in the water looks less bright than before. My almond leaf also doesn't seem to want to sink... it is still floating really well.
I have found that Riley has a fondness for Bumble Bee the transformer... seems to be the most interesting thing he likes to look at.