A)Origin of the metazoa has been clearly elucidated and involves ancestry from a colonial flagellate stock.
B)Metazoans are derived twice.One lineage involves a colonial flagellate stock,and the other lineage involves placozoan-like ancestors.
C)Metazoans arose from a multinucleate ciliate where cell boundaries eventually formed around each nucleus.
D)Placozoans may be similar to the single ancestral state.Features like their small nuclear genome and their large mitochondrial genome are features that may be derived from a common ancestor shared with some animal outgroups.The nuclear and mitochondrial genomes of the Placozoa suggest ancestry with animal outgroups.

A)collencytes.
B)sclerocytes.
C)choanocytes.
D)spongocytes.
E)lophocytes.Spongocytes are archeocytes specialized for secreting spongin.

A)the Devonian period or "age of fishes."
B)the early time of anaerobic prokaryotes.
C)the Cambrian period and probably earlier.
D)the time of the first prokaryotes but the sponges left no fossil evidence for lack of hard parts.Ancestral members of the phylum Porifera arose at least by the early Cambrian period and probably into Precambrian times.Later evolution resulted in diversification into the classes present today.