Hallopora ramosa, Late Ordovician
Ohio

Order Trepostomata

Trepostomes form zoaria that are massive, lamellate-encrusting, or branching. Each zooecium is divisible into an immature region at the axial part of the zoarium and a mature region near the surface. The immature region is characterized by thin walls, wide spacing of diaphragms, and contact with other zooecia on all sides. The mature region is characterized by thickened walls, close spacing of diaphragms, and the intervention of special cells.

Constellaria florida, Late Ordovician, Ohio; Monotrypella quadrata, Late Ordovician, Ohio; Parasopora simulatrix, Middle Ordovician, Kentucky
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Trepostome morphology page 1  |  page 2  |  page 3

Archimedes, Late Mississippian
Illinios

Order Cryptostomata

The zooecia of this group are similar to those of trepostomes, but the boundary between zooecia is much more abrupt and the tubes are much shorter. Diaphragms may be present. The outer zooecium (vestibule) is wider than the inner zooecium.

Archimedes wortheni; Septopora, Silurian, Illinois
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Fenestella althaea, Early Devonian
New York

Order Fenestrata

Zoaria are characterized by erect, unilaminar branching calcareous stems of cylindrical or ribbon form. In many cases, the branches form a meshwork. Unfortunately, the term "fenestrate" is often used to describe any bryozoan with an erect, meshwork structure, when the term "lattice" would be more appropriate. Remember, every bryozoan with a "fenestrate" form does not necessarialy belong to this order.
Fenestrata are sometimes grouped with the cryptostomata.

Fenestella plebeia, Carboniferous
[5]

Fenestrate/Cryptostome morphology page 1  |  page 2

Hederella nicholsoni, Middle Devonian
New York
Encrusting a rugose coral

Order Cyclostomata

The cyclostome zooecia are simple calcareous tubes that usually lack diaphragms. They have a simple, round aperture with no operculum. Zoaria can be massive or delicate branching.

Stomatopora parvipora, Eocene, Mississippi; Corynotrypa delicatula, Late Ordovician, Ohio; Chilotrypa ostiolata, New York; Fistulipora, Permian, Indonesia
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Cyclostome morphology page