Today I present to you a copepod that has been called the most beautiful animal in the world, the Sapphirina. Sapphirins are parasites of gelatinous plankton, especially doliolids, into which they enter and devour. While this fact is terrifying and would make them worthy of a post within this blog, this copepod also has other peculiarities that make it unique within plankton and even within the animal kingdom. To start with, its segmented body is very depressed, thin as a sheet of paper, and goes from being completely transparent to showing iridescences of all the colors of the rainbow. In fact, the name Sapphirina comes from sapphire, which is why they have also been called sea sapphires. The changing colors of their body are achieved thanks to hexagonal crystals of guanine, a chemical compound that most cells use to make the fundamental elements of DNA and RNA. Guanine crystals are also used by other animals, such as chameleons to change color, but in Sapphirines, these changes occur in seconds and are of astonishing intensity and beauty. The role of this iridescence is still a matter of debate in the scientific community. The most widely accepted hypothesis is that since only males can change color and females have more developed eyes, this is a mechanism for attracting the mate. In the last post (The Sexual Life of Copepods) I talked to you about how copepod males detect and trap females to reproduce. Here, it seems to be the female who is attracted to the male, but who would not be attracted to such a splendid light and color show?