The Collaborative International Dictionary of English v.0.48:

Zoodendrium \Zo`o*den"dri*um\, n.; pl. Zoodendria. [NL., fr.
   Gr. zw^,on an animal + ? a tree.] (Zool.)
   The branched, and often treelike, support of the colonies of
   certain Infusoria.
   [1913 Webster]