What the Heck?

Okay, so I keep seeing Socrates with this weird tentacle/psuedopod thing, and (as you can probably guess), I am really confused as to what on Earth it might be or its purpose. He will often climb to a high place, and then it will emerge from under his shell and he'll wave it around. Then he'll pull it back in and climb back down.... I did a little research but didn't find much.If anybody has any idea as to what it might be (fish expert or not,,), please leave a comment below! :) :) 

And.... speaking of Socrates...... Zeus has been bullying him lately. If Socrates is on the gravel at night, he will suck on his shell, and I always have to scare him off with the net. Sometimes, silly Socrates will ctart to climb on to Zeus' face, and Zeus 'strikes' him (I didn't know how else to put it....)