Freshwater and Marine Ectoprocts or Bryozoans: Ectoprocta

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Ectoprocts are similar in appearance to corals, seaweeds, and sponges. They live in sessile (SEH-sill) colonies that resemble jellylike masses, crusts, cups, or plantlike structures. Sessile organisms are attached to one place and cannot move. A colony is any group of organisms that lives together. A single colony may be less than 0.039 inches (1 millimeter) high or grow as tall as 3.28 feet (1 meter). Depending on the species, the outer covering of the entire ectoproct colony is either jellylike or made of chitin ((KYE-tehn). Chitin is the tough, flexible material that makes up most of the external skeletons (exoskeletons) of arthropods (insects, spiders, and their relatives). Some ectoproct colonies are covered with a bony or calcified (KAEL-sih-faid) covering. Calcified coverings are made up mostly of minerals called calcium salts.

Individual animals are called zooids (zu-ihdz). Most zooids are so small that they must be studied through a microscope. Each zooid has a circular or u-shaped lophophore (LO-fo-for) surrounding a mouthlike opening. Lophophores have sticky tentacles covered in tiny bristles, or cilia (SIH-lee-uh). They help ectoprocts to breathe, eat, and protect themselves. Inside, they each have a body cavity, a single nerve bundle, and a u-shaped digestive system. In some colonies, all of the zooids are similar in appearance, but in others, there may be several different kinds. For example, some zooids spend most of their time eating. Others exist only to reproduce or to provide extra support for the calcified skeleton. In some colonies, a network of tubes connects the zooids to each other so they can share digested food.


Freshwater ectoprocts are found on every continent, including Antarctica. Marine species live in every ocean.


Freshwater species are found in shallow, still waters. They attach themselves to the sides or undersides of rocks, wood, plants, and trash. Marine ectoprocts live in shallow waters near the coastline to deep-sea bottoms at depths of 26,900 feet (8,200 meters). They are also found on the surfaces of solid objects, including rocks, seashells, seaweed, and wood.


Both freshwater and marine ectoprocts eat anything, as long as it is small. Most of their food is made up of tiny bits of plants and animals floating in the water and small, living organisms.


The life cycle of ectoprocts includes sexual (SEK-shu-uhl) and asexual (ay-SEK-shu-uhl) reproduction. Sexual reproduction involves males and females producing sperm and eggs. In some groups of ectoprocts, each zooid is a hermaphrodite (her-MAE-fro-dait). Some hermaphrodites have the reproductive organs of both males and females at the same time, while others produce eggs or sperm at different times of their life. Some ectoproct colonies have zooids that do nothing else but produce eggs and sperm. Sperm is released into the water to fertilize eggs that are attached in some way to parts of the colony. In some groups the fertilized eggs develop in special sacs or inside the body cavities of feeding zooids. The newly hatched larvae (LAR-vee) are independent at first. They swim for several hours before they settle and attach to a solid object.


The colonies of many ectoproct species are plantlike in appearance. They were once given the name of moss animals and placed in the phylum Bryozoa. The name Bryozoa comes from the Greek words bryon, meaning moss, and zoön, or animal. Like many mosses, ectoprocts grow in mats or clumps.

Asexual reproduction does not require males or females. Instead, ectoprocts reproduce by budding or breaking off parts of the colony. Each broken piece is capable of developing into a new colony. In some species, these pieces are equipped with special flotation devices that help them to float away and settle in new habitats. Some ectoprocts can only form new colonies by budding.


Freshwater ectoprocts are sometimes a problem when they attach themselves to the insides of water pipes and filters. They can block the flow of water to irrigate fields or prevent filters from removing particles and other organisms from drinking water. Some marine species produce chemicals that are used for medicine and other research purposes.


No species of ectoprocts is considered threatened or endangered.


Physical characteristics: Sea mats form star-shaped or wide sheets of calcified crusts on seaweeds, rocks, and shells. The zooids are longer than they are wide and are sometimes egg-shaped. They have four to twelve spines, giving the colony a "hairy" look.

Geographic range: They are found all around the world in oceans with waters that are not too cold or warm.

Habitat: Sea mats live in shallow marine waters down to approximately 164 feet (5 meters). Their colonies are attached to small species of marine algae (AL-jee) and on the shells of mussels and other mollusks.

Diet: They eat bits of algae floating in the water.

Behavior and reproduction: Very little is known about the behavior of sea mats.

They reproduce asexually by budding. Sexual reproduction involves fertilized eggs released into the water where they hatch into larvae.

Sea mats and people: This species does not impact people or their activities.

Conservation status: Sea mats are not considered threatened or endangered. ∎



Brusca, Richard C., and Gary J. Brusca. Invertebrates. Sunderland, MA: Sinauer Associates, 2003.

Smith, Douglas G. Pennak's Freshwater Invertebrates of the United States: Porifera to Crustacea. New York: Wiley and Sons, 2001.


McKinney, F. K. "Feeding and Associated Colonial Morphology in Marine Bryozoans." Reviews in Aquatic Sciences (1989): 255-280.

Web sites:

The Bryozoa. (accessed on March 29, 2005).

Bryozoa Home Page. (accessed on March 29, 2005).

International Bryozoology Association. (accessed on March 29, 2005).

What Is a Bryozoan? (accessed on March 29, 2005).