Unresolved Whats the difference

I have a little black urchin in my tank. Im not sure if it is a long spine or a rock urchin. Whats the difference in the 2? how can i tell what type i have? Pictures i take of it are always blurry. its about the size of a quarter.

 

Reason i ask is all the pictures i pull up of rock urchins are different. i see ones that look like mine. all black. and then i see some that look different. ill upload a pic on my lunch break

 

http://www.liveaquaria.com/product/prod_display.cfm?c=497 530 3080&pcatid=3080

does it look like this?

 

no its solid black like a long spine but the spines arnt long. per say. looks like on the long spine they are longer than the body is round. but min is like short thin black spines. my guess is long spine but not sure.

 

Here is the best pic i can get he disappears for a few days and then reappears

 

Could be a long spine with broken spines.

I guess the only way to find out for sure is to touch it. If it stings you and hurts pretty bad, it's a long spine. If it doesn't actually inject you with anything than its not a long spine. Lol

 

I have picked it up several times when cleaning only time it ever got me was when i smashed a knuckle into it once and it just felt like a paper cut kinda stung for a few mins then nothing.

 

oh well what ever it is it can stay for now. until it gets to big or starts messing stuff up.

 

Ok so i have gotten the best picture of this guy that i can come up with. he was out and about picking things off the glass so i decided to get a few shots with the led from my phone on.

 

Here are the pics