Step 1 : Introduction to the question "Which is the most abundant vertebrate on the planet?"
...Surprisingly, the most common vertebrate on the planet lives in the darkest depths of the Earth's oceans. The Bristlemouth fish has a population in the trillions or more. This small fish has a slender body only a few inches in length. Like most deep-ocean species, the Bristlemouth fish glows. It has rows of bioluminescent dots that line its abdomen. It uses this as a type of camouflage called counter-illumination. Since little daylight reaches the depths of the oceans, fish appear as silhouettes to predators below them. The bioluminescent dots on the Britlemouth's belly mask its silhouette.Source: Aqua.org.
