Animals that spread like moss
Bryozoans are tiny animals that grow on the surfaces of rocks, plants or animal shells. Thousands can join together to form a mat of identical individuals. They are filter feeders that sieve particles of food out of the water.
Fossil bryozoans date back 480 million years, but soft bodied forms probably existed long before that. They are easily missed as fossils because they usually form a fine, thin layer growing on other fossils. You can see bryozoans in the seas of the Dorset and East Devon coast today. Look for them on the fronds of kelp exposed at low tide.
Below: Living bryozoans on kelp. In the fossil examples, only the base of the animals are preserved, not the delicate filtering structure that extends from them.
Foul or fair?
Bryozoans are often considered a nuisance. They are the first animals to colonise or encrust a surface, including the bottom of ships which causes drag and reduced efficiency. They can also lead to fouling of pilings, piers and docks. But medical experiments are also underway to determine whether chemicals found in bryozoans can be used to fight cancer and other diseases.