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seagrass lagoon

Bryozoans
Phylum Bryozoa

Bryozoans are often mistaken for plants. They look like moss, mats of algae or lacy, branching seaweed. They are quite common on Chek Jawa.

'Bryozoa' means 'moss animals' in Greek. There are about 5,000 species of bryozoans.

Colonial animals: Bryozoans are colonies of minute individual animals called zooids. Each zooid is about the size of a pinhead but has distinct organs and ring of tentacles (called the lophophore) forming a funnel around a mouth. Each zooid builds a hard casing around itself (called a house), usually made of calcium carbonate. The tentacles emerge through an opening to filter feed. The tentacles can be quickly withdrawn into the house and the opening secured with a tiny lid.

The colony forms as the zooids reproduce by budding. Each new casing remaining attached to the colonial members around it. A colony have have millions of individual zooids. Some colonies take the shape of encrusting layers, others develop into delicate, branching forms. So bryozoans are sometimes called sea mats, moss animals or lace corals. They grow over any hard surfaces in the sea, including seaweed and the surface of sand grains.

Bryozoan Food: Bryozoans are believed to feed on bacteria and plankton. Their tentacles are covered with cilia (tiny beating hairs) that generate a current through the lophophore and thus filter out edible titbits. A bryozoan has a U-shaped digestive tract that brings its anus back to the opening in the house, next to the lophophore, for waste disposal.

Bryozoan Rebirth: Each individual zooid may completely degenerate within its house and is later regenerated again by the house. Remains of the old zooid might be consumed by the new zooid. Each zooid might do this 4 or more times. In a single colony, various zooids might be at one of these stages of death and rebirth.

Bryozoan Babies: A bryozoan colony grows by budding, but bryozoans also reproduce sexually. Most bryozoan colonies are hermaphrodites, but each zooid usually either male or female. Most bryozoans shed their sperm into the water but brood their eggs. The parent zooid usually degenerates as the embryo develops. It may later be regenerated after the free-swimming larva literally leaves the house. These eventually settle down and start a new bryozoan colony. Some produce a particular kind of larva called cyphonautes that is enclosed by a pair of shells and can remain drifting for many months. Here is a photo of bryozoa cyphonautes on Image Quest 3-D Marine Library.

Human uses: Being immobile, bryozoans may help protect themselves with chemicals which deter potential predators. Some of these chemicals are being studied for human medical applications. A bryozoan compound is part of the drug bryostatin which is being tested as an anti-cancer drug.

quick facts
Comes in various shapes and forms, found in the seagrass lagoon and coral rubble area

Classification:
Phylum Bryozoa

See also ...
Sponges look like ascidians but are much simpler creatures
Hydroids are sometimes mistaken for bryozoans and visa versa.

Links
Flowers of the Sea: Bryozoans by Jean-Marie Cavanihac on the Microscopy UK website: fact sheet on bryozoans with lots of lovely super close look at tiny bryozoans.
Bryozoa on the Museum of Paleontology, University of California, Berkeley website: details with photos.
What is a Bryozoan? on the Smithsonian Marine Station at Fort Pierce website: detailed technical introduction to bryozoans and lots of fact sheets on various species.
Lowly creatures from the deep may help cure cancer and warn of pollution by Mark Shwartz on the Stanford University website: a layman's article on the development of bryostatin as an anti-cancer drug.
Photos of a variety of bryozoans on the San Francisco Bay page of the California Academy of Sciences website.

Other references

Barnes, Robert D. & Ruppert, Edward E., 1996. Invertebrate Zoology. Harcourt College Publishers. 6th Edition. pp. 1056, G-1-16, I-1-30.
Pechenik, Jan A., 2000. Biology of the Invertebrates. McGraw-Hill Book Co., Singapore. 578 pp.
Tan, Leo W. H. & Ng, Peter K. L., 1988, A Guide to Seashore Life. The Singapore Science Centre, Singapore. 160 pp. online version

a companion website to the chek jawa guidebook website©ria tan 2003 www.wildsingapore.com

a companion website to the chek jawa guidebook
website©ria tan 2003 www.wildsingapore.com