(Lower Cambrian-Lower Devonian)

Chitinozoa are extinct marine microscopic fossils with organic-walled skeletons called tests or vesicles, measuring 0.05-2.0 mm in length and resembling miniature flasks.  They are of uncertain affinity but are treated taxonomically as animals, probably monophyletic.  Chitinozoa originally occur as single tests.  Some scientists believe that Chitinozoa are marine metazoan egg capsules, similar to gastropod egg capsules.  This is based on their frequent occurrence in aggregates or in chains, joined in an aperture-to-base formation.  This linear assemblage is widespread in all the common genera.

The Chitinozoa were named after their chitinoid appearance in 1931 by the German micropaleontologist Alfred Eisenack, who discovered multiple genera in 1929.  Chitinozoa are classified according to the overall shape of the test, ornamentation, the essential qualities of the basil margin, the tendency to occur in chains, the nature of the internal prosome-operculum structure, and size.  More than 50 genera and 500 species have been described. 

Chitinozoa appeared during the late Cambrian, diversified rapidly in the Ordovician and Silurian Periods, and became extinct toward the end of the Devonian.  Chitinozoa are generally accepted to be planktic.  This is supported by their broad geographic distribution and occurrence in a wide range of depositional environments.  Moreover, they are preserved in most types of marine sedimentary rocks.  These characteristics, in addition to their rapid evolution, make chitinozoans for both regional and intercontinental stratigraphic correlation.