Many species need to live with others of their kind in order to survive
 

•  Humans beings are very dependent on the other humans they live with although this tie is primarily cultural
• Wolves live in a tighter collective in which the colony has to work as a unit to kill prefered pray.  Moreover,  the Alpha couple generally produces all of the offspring, although other wolves are biologically capable of having pups.
• Bees are still closer.  All of the inhabitants of the hive are siblings because there is only one female in each colony capable of reproduction.
• The bryozoan and coral colonies we find in Nashville are the tightest colonies of all.  Since they reproduce asexually within a colony, all individuals in it are clones (twins) of each other.

Identifying colonial animials is difficult.  Bryozoans are particularly difficult to identify since the inividual animals, zoids are so small and colonies can
take a variety of forms.   Bryozoologists cannot definitively identify a bryozoan without looking at a thin section under a microscope.  Since I don't have
the equipment to do this, all of my identifications are tentative.

You can give your students a feel for what scientists see when they look at bryozoans by looking at them under a microscope or even under a 10X hand
lens.

Studying bryozoans, however, is a good way to see the wide variety of forms  that colonies can take. In general, they take four forms:
 

• Tree-like bryozoans: These bryozoans formed complex twig or branch- like structures. Colonies sometimes start by encrusting over a shell and then sending up branches.
• Frond-like bryozoans:  These bryozoans form paddle or leaf shaped structures which grow like a head of leaf lettuce.
• Encrusting bryozoans:  Some bryozoans grow as thin colonies over other animals.
• Free-standing bryozoans: Some bryozoans formed thick multi-layered colonies over the shells of other animals.

Study these bryozoans and see if you can classify and describe the colony.
 
 

	This is Heterotrypa. It is a frondlike bryozoan, and is probably the most common bryozoan in the upper Ordovician Leipers Formation, in Nashville.
	This is Hallopora.  It is a small tree-like bryozoan.  There are two species; one with ridges and one with bumps.  It is found in the upper Ordovician Liepers Formation
	This is Atactoporella.  It is an encrusting bryozoan which grew on small snails.  In Nashville, it is found only in the Hermitage Formation and the bottom of the Middle Ordovician Nashville Group (about 10 million years earlier than the two bryozoans above).  There are similar encrusting bryozoans alive today.  They have symbiotic relations with their host.
	This is Constellaria.  It forms both tree-like and frond-like colonies.  It can be identified by the small star-shaped decorations.
	This is Prasopora.  It is a free-standing bryozoan, which grows on the shells of small mollusks and brachiopods.  it is found in the Hermitage Formation at the base of the Nashville Group.  These colonies are not thin like Atactoporella, but have many layers, forming rings on the botom (concave) sides.  They get much larger than the host animal.  No brachiopod or mollusk could survive with a Prasopora colony on it.
	This is Homotrypa.  It is a tree-like undecorate bryozoan, common in the Leipers Formation.  One of the most interesting charactics of this bryozoan is that it often grew on the sehll of a large bivalve mollusk called Byssonychia.  I often find Homotrypa fossils with an external mold fossil of Byssonychia on the bottom.