wierd things living in my tank

[cichlid101]

Can anyone identify these critters. They only come out at night and disapear when the light comes on. I have about five of them in the tank. They live in the LR and shrivel up into a hole or crack when the lights turn on. I am posting 3 pictures for you to view for your pleasure. They are about the size of a quarter and a few dimes and two pennies.
Thank you for your help.

 

[cichlid101]

number 2

 

[cichlid101]

number 3

 

[cichlid101]

i thought urchins were hard shelled and not jelly form. what kind of urchins?

 

[asbury030]

What do u guys mean by bump this up?

 

[asbury030]

oh ok thanks

 

[cichlid101]

so is that a good thing or bad thing?