Question: What is the smallest animal in the ocean?

Steve Thackeray answered on 19 Jun 2020:

Good question Abigail! The ocean is full of tiny creatures that you would need a microscope to see properly. These organisms are called “plankton” – this is a nice introduction, if you can view it: https://oceanservice.noaa.gov/facts/plankton.html. The animal members of the plankton are called zooplankton, and include tiny little crustaceans, molluscs, worms and jellies. Even smaller than these are organisms that aren’t technically animals, like bacteria for instance. These tiny organisms have roles similar to those for larger animals – some are like herbivores, and some are carnivores. They can compete for food, migrate, and search for mates. Plankton are just fascinating, and not just found in the ocean – there are freshwater plankton in lakes, ponds and slow-flowing rivers too.