Copepods go through many transformations during the course of their planktonic lives. Hatching from an egg which might be attached to the adult female or deposited into the water, the first stage of copepod life is called a nauplius, transitioning into the more mature copepodid form and then the final adult stage.
The naupliar stage of the copepod is smaller and looks vastly different than the adult form, consisting of just a head and tail with the thorax and abdomen absent. This form lasts for 5 or 6 moults (depending on the species) before reaching the copepodid stage.
The copepodid stage is when the animal finally starts to resemble what we recognize as a copepod, gaining a thorax and abdomen, although these are not as complex as what is found in the adult. After five more moults as a copepodid larva the copepod finally reaches the adult stage. The time it takes to mature for different copepod species varies greatly, ranging from a week to a year.
Mating consists of the male grabbing the female with his first pair of antennae and transferring a sperm packet to the female’s genital opening with his thoracic limbs, continuing the cycle.
Although most of the stages of life are too small to be seen with the naked eye, the variance in copepod form is a good thing for your tank, as it ensures that your reef inhabitants have plenty of different prey to choose from, both in the water column and on the tank's surfaces. Studies have shown that larval fish prefer to feed on the nauplius in their first few days, and as they grow they will incorporate the larger, harder to catch copepodid and adult stages into their diet.
Image Source: https://www.st.nmfs.noaa.gov/copepod/about/images/copepod-lifecycle.jpg