What you are looking at:
Is a shark.
The smallest species of shark in the world. It is called the dwarf lantern shark. They are in fact a carnivore, though it might be hard to tell from its size.
They typically feed on small crustaceans.
They get their name due to their size and their special ability:
Their belly can glow in the dark.
It is designed to help hide them against the backdrop of the rippling surface above, making them invisible to many prey below.
The light glowing belly also attracts much prey to them, making them easy food for this beast.