Cuschieri, 2002 Mesodermal organ Mesoderm (muscle) Ectoderm Ectoderm Parenchyma (mesoderm) Gut (endoderm) Acoelomate Mesodermal peritoneum Gut Mesentery Ectoderm Coelom Mesodermal organ Mesodermal organ Pseudocoel (from blastocoel) Gut (endoderm) figure 9.