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Fossil Bryozoans

Fossil bryozoans first show up in the fossil record during the Ordovician Period. They probably existed earlier, however, in soft forms that did not secrete hard enough exoskeletons that would leave fossil evidence. They quickly evolved into many species, eventually spreading throughout the globe in both marine and freshwater environments. Because they create homes of calcium carbonate and are so plentiful they are responsible for reef building. Bryozoans may be the most abundant fossils on earth! They have thrived in every time period since the Ordovician and continue to be an abundant life form in the present.

Bryozoans are microscopic invertebrates that live in water. They are commonly known as moss animals. There are many different species of bryozoans that typically live in groups, called colonies. Bryozoans can attach themselves to rocks, or tree branches that have fallen into the water. Different species can look pretty different from one another, often making it hard to identify. Some colonies are smooth and rounded, similar to jellyfish, while others resemble antlers or mosses. They can also spread themselves, like vines across rocks, or create furry colonies.

We currently have 2 fossil bryozoan species available for sale:
Archimedes a fenestrate bryozoan colony. Fenestrate means they built lace like structures for their homes. The zooids lived in tubes in this structure which was attached to a screw shaped support. The fossil that you see is this support structure. This fossil is from the Mississippian Epoch of the Carboniferous Period and is about 324 million years old. 

Heterotrypa subfrondosa a branching bryozoan from the Ordovician Period. They are about 450 million years old and were found in Carrol County, Kentucky.

Bryozoans come in all shapes and sizes. Individual bryozoan is called a zooid. Each zooid attaches itself to a surface at its base. Since individual zooids require some type of magnifying instrument, they are usually measured by colony size. Colonies range in size from 1 centimeter to nearly 3.5 feet.  However, the majority are under 4 inches across. The shapes of colonies vary widely, depend on the pattern in which they grow, the variety of zooids present and the type and amount of skeletal material they secrete.

Its body has an outer structure, called a cystid, that looks kind of like a sleeve. This includes an opening at one end. This could be thought of as the ‘mouth,’ where food enters. A mass of organs, called polypide, moves within the cystid. 

Bryozoans have a very interesting way to eat: from the inside out. The cystid permits the polypide to slide outward toward the water. This process exposes a headlike structure called a lophophore, crowned with tentacles, which filter food from water. Bryozoans eat other microscopic organisms from the water. Little hairs, called cilia, line the tentacles and sweep the food into the mouth.The tentacles and polypide are very sensitive, and will react at the slightest bump.

Bryozoans are truly remarkable little creatures, and it is unclear how they are related to other invertebrates. It’s as if they stand on their own in the animal kingdom.One hypothesis is that bryozoans evolved from a marine worm. 

Most bryozoans live in salt water, however there is one class of them called Phylactolaemata, that live only in freshwater. About 20 unique species of bryozoans live on our continent. They usually are prefer quiet waters of lakes, ponds, and swamps, but some live in streams. Most bryozoan colonies are sessile, meaning they attached to some object, such as a rock, dock support, or tree branch, but some species do not attach to objects. Most of this type form in spring and die away in winter. Colonies reach their largest size in late summer and fall, which is when most people notice them.

Freshwater bryozoans are harmless, though they occasionally clog water pipes and sewers. However, other species are harmful to fish, causing kidney disease in salmon and their relatives. Don't worry, they can be helpful too. Like mussels and other filter feeders, they gradually cleanse the water as they feed. Also, their presence usually indicates good water quality.

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