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VMNH Bryozoan Page

Introduction to Bryozoans

Bryozoans are colonial animals.

Individuals (called zooids) are connected in colonies.  Colonies grow by budding new individuals at the edges.

Individual bryozoans are microscopic, but their colonies can be quite large.


Watersipora colony with tentacles of zooids extended to feed.

More than 5000 bryozoan species have been found so far (That's more than all the mammal species in the world).

There are probably at least that many more to be discovered.


What do bryozoans look like?

Many colonies look like hard crusts or fuzzy mats attached to objects in the water, giving them the common names of  sea mats or moss animals.

Other bushy branching colonies look more like seaweeds.


Where do bryozoans live?

Bryozoans live in almost every kind of benthic (sea floor) habitat in the ocean, from the shore to the greatest depths.

On sandy beaches (like Virginia Beach) you would be most likely to find bryozoans living on shells, mermaids' purses (skate egg cases) or the molted shells of horseshoe crabs.


On rocky shores or reefs colonies encrust seaweeds or the undersides of rocks or corals.

On sandy or muddy sea floors rooted bryozoans (like these from Antarctica) can be the most abundant animals present.

They are very common on floating plastic trash and on ships' hulls, hitching a free ride for hundreds or thousands of miles.

They are also found in fresh water where their colonies are attached to the undersides of rocks as well as submerged wood and the leaves of pondweeds.   Some freshwater bryozoans, like Pectinatella, form massive colonies in ponds and reservoirs in late summer and early fall.

Other freshwater species form inconspicuous networks like those of Plumatella.


Fossil Record of Bryozoans

Bryozoans have existed for hundreds of millions of years (since the early Ordovician) and are common fossils in marine deposits.


How do Bryozoans Live?

All bryozoan colonies have feeding individuals with  a funnel of ciliated tentacles to filter small particles of food from the water. The tentacles can be withdrawn into the protection of the zooid.  In cheilostomes the opening through which the tentacles protrude is a trap-door like hinged operculum.

In addition to feeding individuals colonies may have zooids specialized for other functions.  Some cheilostome bryozoans have individuals with no feeding parts, but with an operculum shaped into a bristle (called vibracula) for cleaning or moving the colony.
Others have opercula and zooids modified  into pincer-like structures (called  avicularia) capable of snapping shut on a trespasser or predator. 



Other zooids are specialized for reproduction and may have brood chambers called ovicells in which embryos develop into larvae.  The larvae swim away from the parent colony and find a new surface (like a bit of shell or a rock) to which they attach.  There they metamorphose into the first individual of a new colony which begins to feed and to bud additional zooids.  

bryozoan larvae


What good are bryozoans?

One of their roles is to serve as part of the ocean's natural filtration system.  Like an aquarium filter system, the feeding activities of bryozoans and other filter feeding animals strain out excess food and debris particles to help keep the water clean.

Bryozoans may also be medically useful.  Adults of bryozoans and other colonial animals like sponges, corals, sea fans, sea squirts, hydroids, etc. are solidly attached in one place.  Like plants they cannot run from predators.  So, like plants, many of them have developed chemical defenses that discourage other animals from eating them, or protect them from disease.  We have always obtained many medicines from plants.  Now we are beginning to discover medicines from marine animals.

This bryozoan, Bugula neritina, produces a chemical called bryostatin.  We don't know what it does in a living bryozoan, but cancer researchers have found it to be active against leukemia and a number of other kinds of cancer.  Bryostatin is now being tested in  clinical trials.


What problems are caused by bryozoans?


Bryozoans are one of the main groups of fouling organisms, animals and plants that encrust ships, piers, buoys and other man-made structures in the oceans.    One of the biggest problems in marine biology today is the invasion of marine habitats by alien species.  Now, in addition to transport on ships' hulls, marine animals are often spread when ships dump ballast water containing their larvae thousands of miles from its original source.  Marine taxonomists are taking part in rapid assessment surveys to determine the spread and persistence of exotic species which may wreak economic and environmental havoc in the marine ecosystems they invade.



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