Bryozoan skeletons grow in a variety of shapes and patterns: mound-like, lacy fans, branching twigs, and even corkscrew-shaped. Their skeletons have numerous tiny openings, each of which is home to a zooid. They also have a coelomic body with a looped alimentary canal, or gut, which opens at the mouth and ends at the anus. They feed with a specialized, ciliated structure called a lophophore, which is a crown of tentacles surrounding the mouth. Their diet consists of small microorganisms, including diatoms and other single-celled algae. In turn, bryozoans are preyed upon by grazing organisms such as sea urchins and fish. Bryozoans do not have any defined respiratory or circulatory system due to their small size. However, they do have a simple nervous system and a hydrostatic skeletal system. Several studies have been carried out on the crystallography of bryozoan skeletons, revealing a complex array of oriented calcite or aragonite
hong kong email list crystallite fabrics within an organic matrix; see, for example, Hall et al. (2002).
The tentacles of bryozoans are ciliated, and the beating of the cilia creates a powerful current of water that drives the water along with entrained food particles (mainly phytoplankton) towards the mouth.
Because of their small size, bryozoans do not need a blood system. Gas exchange occurs across the entire body surface, but particularly through the tentacles of the lophophore.
Bryozoans can reproduce both sexually and asexually. All bryozoans, as far as we know, are hermaphrodites (meaning they are both male and female). Asexual reproduction occurs by the budding of new zooids as the colony grows, and is the primary way in which a colony expands in size. If a piece of a bryozoan colony breaks off, the piece can continue to grow and will form a new colony. A colony formed in this way is composed entirely of clones (genetically identical individuals) of the first animal, which is called an ancestrula.