Part of diving and photography is to understand the actions of the subjects you are looking to get images of. For some its fairly obvious that its a mating ritual. Take the cuttlefish for example, they dance around, flash some colours and get jiggy with it. Whilst their appendages may not be human you get the idea of whats going on..
But coming across this striate anglerfish doing a one arm handstand in a sponge, you wonder what was going on its mind. There's no missus anglerfish nearby, so perhaps he's just showing off or keeping trim for when she does come along.
The one below was going for a little walk, then began to lean forward on its front legs and kick its back legs in the air. If you have ever seen a friend 'do the worm' on the dance floor, then its kinda like that.
Whatever they are doing its pretty amusing to watch.