O.k., there is a reason people don't ask me to approx. size and distance... I got out a ruler and held it up to the tank, the mantle is more like 3-4 inches. I don't think the webbing extends all the way down the arm when it is spread. It totally does the skunk stripe thing on the mantle, and there are some "eyespots" on the mantle up above the siphon. There are some SMALLISH white spots above the arms, but nothing dramatic. I am going ahead and saying it is diurnal, just shy. As I mentioned before, when we walk into the room and it's alone, it is active on the glass and light grey. Right now it is watching me watch it, and is mimicing the live rock it is on. This one has the ability to look so much like the live rock that you can be staring straight at it and can't see it, but then maybe if Al hadn't been older he'd have done that, too. I can see that the tip of the first arm is blunt, maybe lost and grown back.