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Today on Animal Fact Files we’re discussing copepods. Copepods are typically tiny, nearly microscopic crustaceans that make up a large majority of plankton in waters around the world. The term 'plankton' applies to organisms in the water that are unable to swim against a current. Along with other animals like rotifers, krill, and even jellyfish, copepods make up the collective group known as plankton. They can be told apart from other plankton by their cylindrical, tube shaped segmented body and their segmented appendages which they use to move around. Many have long, obvious antennae and a single, red eye - much like the most well known of all copepods. Of course, not all copepods have an eye; heck they don't even all live in the ocean.

There are currently more than 10,000 described copepod species. They live in marine waters, brackish estuaries, freshwater lakes and rivers, swamps, including surrounding moist leaf litter and damp soil, collected water in plants like pitcher plants, and even caves where eyesight isn't necessary! They range from the tallest mountain ranges to the deepest oceans from icy seas to tropical beaches. Like nematodes, these animals are found almost everywhere! Most copepods are planktonic throughout their entire lives, though some species are benthic as adults meaning they live on the floor of their respective body of water. Sometimes these animals are known as the insects of the sea, however it should be noted that virtually no insects actually live in the ocean, and, because copepods are found in many other places, we're not too fond of that name.

Most copepods are a millimeter in length or smaller, but some free-living species can reach up to a centimeter long. These are usually found in colder areas. Parasitic copepods top the charts with some species reaching over a foot (30.5cm) long! Copepods are often transparent, but they can take on different colors based on what they eat. These invertebrates eat other planktonic organisms including fish eggs, algae, and even each other. Like flamingos, carotenoids from their meals change the copepod's hue. Some copepods are parasitic, as well. They'll attach to another animal like a fish as displayed on this video's thumbnail and in the current video on screen. Copepods may travel to the surface at night to feed when they're not as easy for predators to spot. Then, as morning comes, they'll sink down into the dark depths, sometimes diving deeper than 1,000 feet below the waves! This helps them avoid predation. All kinds of animals eat copepods from fish like seahorses to the largest living mammals on earth! They can even have their own parasites!

Copepods begin life as an egg. Males are described as slightly smaller than females and have modified first antennae for delivering sperm. The female's eggs are fertilized and often brooded in a sac that is attached to her body, though some species release their eggs. Depending on the species and the surrounding water temperature it can take a few days to a few months for the eggs to hatch. After hatching, the larvae that emerge look nothing like the adults. This is known as naupliar stage, and it's shared among other crustaceans like barnacles, lobsters, and crabs. It takes a few molts before they start to resemble their adult form and a few more before they're reproductively mature. Most copepods only live a year or less, but longer developing species can surpass this.

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