Please ID - Invertebrate

[Alex V.]

Its about 4" long and 3/4" wide. It just show up dead on the sand bed. I have never added such creature to the tank nor I have added any live rock since I started the tank with dry rock 7 years ago. I think its a pink and black sea cucumber I added 5 years ago, but it does not looks quiet like it.

 

[vetteguy53081]

Looks very close to a kumquat sea cucumber but is not

 

[Rtaylor]

Cryptoplax larvaeformis, it’s a type of chiton

 

[DaJMasta]

Looks like a match too me, too bad the cool big guy died!