In this photo you can see many Crown Squirrelfishes (sargocentron diadema) under a rock. Squirrelfish are also known as Soldierfish. They can often be seen in the shallower parts of the reefs. During the day, they are hidden in the cracks of the reefs. At night they roam over open sand and low-profile reef areas to feed of shellfish, polychaetes and small crabs.
Crown Squirrelfishes are rather small, their size rarely exceeds 13 cm, but you should not play with them either, because they have a venomous spine on its preopercle.