Info Please help to identify this creature

[Seaweed Doc]

iNaturalist first suggestion is Elysia, but I'm skeptical.

After Elysia, it's suggestion is Acanthozoon. (Watch spelling.)

I'm pretty convinced it's Acanthozoon (a flatworm), but I'm not perfect as my wife reminds me.

 

[Umuntu]

Looks like a giant clam mouth or some type of clam. Hard to see amidst the coral.