UGA Stratigraphy Lab

The data is in the strata

A guide to identifying trepostomes from the type Cincinnatian


Although the external growth form of a trepostome is the most obvious feature, internal structures are the most critical for identification. Because these structures must be revealed by making thin sections or acetate peels, bryozoan identification is commonly thought to be difficult. Furthermore, thin sections and peels are sections through a three-dimensional structure of initially unfamiliar parts, adding to the complexity of identification. Even so, identification of bryozoans is not that difficult. This guide will show you how.

Start with the growth form

The first step in identification is to use the growth form to narrow the list of possible genera.

Ramose trepostomes

First, check to see if any of these distinctive features occur:

Are there cystiphragms?

Are there blunt hemiphragms?

Do the zooecia in the endozone have square cross-sections?

Are there star-shaped monticules?

Are there wide zooecia in the central endozone that markedly thin before the exozone?

If none of those are present, check for mesozooids:

Are there abundant mesozooids with many diaphragms?

Are mesozooids present but not abundant?

Are mesozooids absent?

Leaf-like (frondose or bifoliate) trepostomes

Are there cystiphragms in overlapping series?

Are cystiphragms absent?

Encrusting trepostomes

Are there cystiphragms in overlapping series?

Are both styles and diaphragms abundant?

Are styles abundant, but diaphragms sparse or absent?

Are styles sparse to absent?

Hemispherical and disk trepostomes

Are there cystiphragms in overlapping series?

Does it lack cystiphragms in overlapping series?

Massive trepostomes

Are cystiphragms in overlapping series present?

Does it lack cystiphragms but have well-developed styles?

Does it lack both cystiphragms and styles?