Bryozoans (Phylum Bryozoa) comprise a group of clonal, modular (“colonial”), mostly sessile, mostly marine animals.
Most bryozoans excrete a calcareous exoskeleton, and as a result the group has an extensive fossil record that began late in the Cambrian Period ~490 million years ago, making it useful for evolutionary studies.
SEM image of a silicone cast made from colony mold of a Cretaceous bryozoan fossil (ca. 100 million years old) collected on Goshoura Island, Kyushu, Japan. Shown is the frontal surface of he skeleton of several zooids, each about 0.5 mm long.