Cheilostomata Hippoporinidae Hippoporina SEM of Hippoporina verrilli, an encrusting bryozoan. Note the pores perforating the frontal surface, and the distinct umbo inferior to each orifice. Photo by J. Winston, courtesy of the American Museum of Natural History. Used with permission. H. verrilli colonies are calcified and encrusting.
Individual zooids are regular in shape, and generally quadrangular.
Zooids measure an average of 0.40 X 0.29 mm, but older colonies grow as large as 0.47 X 0.39 mm. A slightly raised rim separates zooids from each other. Ten to twenty regularly-spaced pores perforate the frontal surface of individual zooids. The orifice is rounded distally, with a slightly curved proximal portion. There is often an umbo just inferior to the orifice.