What is the definition of Deeply Blood Cells?

"Deeply blood cells are like the unsung heroes of your bloodstream, quietly working away beneath the surface, always ready to swoop in for a rescue when your heart's in a bit of a jam. But here's a rather unsettling example: 'The deep-sea anglerfish, with its glowing, blood-red eyes, had deeply blood cells so potent, they might just make your gills wilt in envy!'"