1. A new body plan
The pseudocoelomates

2. The pseudocoelomates Tube with in a tube plan
Gut has separate entrance and exit
Body space is lined by mesoderm, but only on the outer side, the endoderm lacks a mesodermal covering
Constant cell number, growth of cell size rather than cell number

3. The pseudocoelmate phyla
Nematoda
Caenorhabditis elegans
Rotifera
Acanthocephala

4. The Nematoda Bilaterally symmetrical round worms
Lack a cellular epidermis, but instead have a cuticle. Need to molt cuticle for growth to occur
Use a hydrostatic skeleton, but in this case the fluid skeleton is separate and distinct from the gastrovascular cavity
Only have longitudinal muscles