I'm.......speechless! Sort of looks like a developing embryo! I see the hand, don't want to even wager a guess on the two pointy things above, Wow! Was there a name other than "13"?
This was FUN.

Leelee - It's a marine gastropod mollusc (snails etc.) that lacks a shell and is called a nudibranch or sea slug. This one is a member of the Family Dorididae. The red tuft at the back is its gills and the two projections on the front are sensory antennae. Like snails, they have a sort of rasping More...

Nudibranch translates as "naked gill" and refers to the fact that the gills are exposed rather than enclosed in the shell. Just for some more trivia, the group of gastropods to which they belong is called the Opisthobranchia, which means "rear-gilled".

Neither a clown nor a mutant be,
Just some creature from under the sea.

I completed the puzzle before reading the comments and I was off into the symbolism of almost human shapes in blue and black garments on yellow and black beach towels. It was quite disappointing to realise that it was a 'real thing' even if it looked unreal! Good fun