Yep, please do check out the shell. That's a beauty you have there, no matter what species (or hybrid) it turns out to be, and a huge one, to boot!:eek1:
Here's a little more identification help:
Hippopus hippopus 15.75 " - 17.72 " (40cm - 45cm)
Hippopus porcellanus up to 15.74 (40 cm)
http://www.sealifebase.fisheries.ubc.ca/summary/Hippopus-porcellanus.html
Tridacna costata up to 15.74 (40 cm) (extremely endangered)
Tridacna crocea 7.87 " - 9.84 " (20cm - 25cm)
Tridacna derasa 15.75 " - 23.62 " (40cm - 60cm)
Tridacna gigas 39.37 " - 51.18 " (100cm - 130cm)
Tridacna maxima up to 11.8" (30 cm)
Tridacna mbalavuana up to 19.68" (up to 50 cm) (Syn: Tridacna tevoroa)
Tridacna noae up to 11.8" (30 cm)
Tridacna squamosa 13.78 " - 15.75 " (35cm - 40cm)
https://cites.unia.es/file.php/1/trainers/E-GC Briefcase-20.ppt
A pretty light version of identifying clams from CITES. Some of the photographs I'd question if they were accurate portrayals, but it is what it is. The information on the shell scutes may be helpful to determine the dominant species if it's a hybrid.
Here's a shot of my old Viet Squamosa when it started out
and another shot a few years later next to a tear drop maxima - the Foxface was full grown, about 8" at the time.
Take a few more pictures and post them, though - I'd never get tired of looking at a nice specimen like that!
Cheers,
Ray