choanoflagellates
single-celled eukaryotes; marine organisms; feed by ingesting bacteria; can form simple multicellular groups that beat their flagella to draw food particles in water past cells; close evolutionary relationship to animals, suggesting that earliest animals
sponges
evidence of connection between animals and choanoflagellates in that. they have cells resembling those of chonaoflagellates but are multicellular; body plan of a flower vase with small pores along its sides and large opening on top; interior surface lined
choanocytes
collar cells that line the body cavity and have flagella that in coordination circulate water in sponges to bring food to inner cavity and exchange carbon dioxide for oxygen; similar to choanoflagellates in that they have a collar of small cilia around fl
mesohyl
a gelatinous region between the two layers of cells of a sponge; noncellular, but contains amoeba-like cells that form skeleton, help with reproduction, and disperse nutrients; where reproductive cells undergo meiosis and differentiate into sperm or eggs
spicules
small, spike shaped particles of calcium carbonate or silicon dioxide that make up the skeleton of some sponges
Eumetazoa
clade that includes most animals
cnidarians
one major branch of Eumetozoa; body plan includes radia symmetry and a mouth surrounded by tentacles with stinging cells; digest food by taking it into specialized, closed compartment and using enzymes in cells lining walls of compartment; can eat large f
diploblastic embryo
embryos with 2 germ layers (epidermis and endodermis)