Why do soft-bodied tunicates leave few fossils?

Tunicates leave a sparse fossil record primarily because they are soft-bodied animals. In paleontology, the preservation of an organism typically requires the possession of hard, resistant parts—such as shells or skeletons—that can withstand decay and geological processes. Because most tunicates lack these durable structures, they are rarely preserved in the Earth's crust.123

The only notable exceptions are certain species that possess hard mineral particles known as spicules within their tunics, which may occasionally be preserved. Generally, for soft-bodied organisms to enter the fossil record, they require exceptional conditions, such as rapid burial in sediment to prevent decomposition or scavenging, or specific environments that allow for the formation of impressions or carbonized films.123