Classes of the Phylum Bryozoa (currently in Atlas)


What is a bryozoan?
Specimens of bryozoans are some of the most abundant fossils in Cincinnatian strata.  Bryozoans comprise a phylum of tiny animals (<1 mm each) that build calcareous colony structures.  These colonies may grow into free standing mounds or branches or they may encrust shells of other animals.

Although bryozoan diversity and abundance is less now that in the Ordovician, bryozoans are still common in the world’s oceans. Modern bryozoans tend to form small colonies in warm water with the largest colonies growing under cool water conditions.

Physical attributes
Bryozoan colonies can develop into a wide variety of shapes which results in complex terminology to describe details of colony morphology.  Separate pages are dedicated to bryozoan morphology and its associated vocabulary:

Bryozoans versus corals
Among Cincinnatian fossils, bryozoans are most often confused with colonial corals.  These groups, however, are not closely related and have fundamentally different body plans.  The simplest way to differentiate corals and bryozoan fossils is to examine the size of openings in the colony structure occupied by individual animals.  Bryozoan animals are very small and the individual zooecia are similar in size the tip of a needle and often require magnification (such as a hand lens) to discern clearly.  Individual coralites, however, are much larger and are easily differentiated with the naked eye.