an order of extinct marine bryozoans. The order, which encompassed 120 genera, existed from the Ordovi-cian to the Triassic. Trepostomes lived in massive hemispherical, lamelliform, or branched colonies. There were two regions in a colony—immature and mature. The immature region, the axial area of the colony, had thin-walled prismatic tubules of auto-zooid cells. The mature region, which constituted the periphery of the colony, was characterized by autozooid tubules bent toward the exterior, thickened walls, and numerous diaphragms. Besides autozooids, the colony had representatives of various heterozooids, which created mesopores, acanthopores, and mi-croacanthopores. The cell walls were threaded with a system of capillaries.
The Trepostomata are significant in answering questions of the stratigraphy of the Ordovician and Silurian.