How many animals swim in the sea? It's not easy to count them all. To get a feel for the ocean's diversity, scientists, such as those involved in the Census of Marine Life, sail out on research cruises to collect and count as many animals as they can find! Shown here is a sample of zooplankton collected in a trawl net with a 10-meter-square opening, including a jellyfish, a lanternfish, a snipe eel, two large orange shrimp, a fuzzy pyrosome (which is bioluminescent), and several smaller animals. Read about how scientists estimate the number of ocean species that haven't been discovered yet.