@Mr Gharial It's the name of the species because it bores into the rock it attaches to, which affords some additional protection - as this is the smallest species (rarely exceeding 15cm across), it cannot rely on sheer mass to avoid predation like the larger Tridacna species can.
This species is very common in my experience, even on degraded reefs like where I saw this one. Often you'll find them in small clusters of 2-4 individuals, but this one was solo. Even though they are common, I keep an eye out for them as the mantle colouration and patterning is highly variable, and particularly pretty ones make for nice close-up shots.
