Origin of the Cnidaria (Coelenterata)

Alternation of generations
polyp (asexual) with medusae (sexual)
planula larvae
sting cells cnematocysts

Platyhelminthes (flatworms)
freeliving, flukes, tapeworms
triploblastic
mesoderm
acoelomate
enteron=gut cavity incomplete
acellular ciliated creature into a multicellular ciliated creature

Nematoda
worm-like
complete gut
coelom is pseudocoelom
cuticle
constant cell number

Annelida (segmented worms)
Oligochaetes, Polychaetes, Hirudineans
segmented body cavity (coelomate)
complete gut