∞ generated and posted on 2016.02.25 ∞
The roundworms.
Members of phylum Nematoda, the roundworms, are triploblastic animals possessing pseudocoeloms rather than true body cavities.
Most animals are triploblastic, meaning they possess three primary germ layers – ectoderm, mesoderm, and endoderm – which are basically the outside, the middle, and the gut lining, respectively.
What makes roundworms unusual, in this regard, is that the middle part is not well attached to the lining part. The result is a volume found between the mesoderm and endoderm and this volume, or body cavity (or coelom), is called a pseudocoelom.
Beyond possessing a pseudocoelom rather than a true coelom, the roundworms are not terribly sophisticated mesodermally, that is, in terms of their musculature. That is, and as a consequence, these are animals that can slash its body around back and forth but are not terribly sophisticated beyond that in terms of its movement.