They have three germ layers but no distinct head region.

Their development restricted to aquatic environments only.

They have body organisation with radial symmetry around a central axis.

They have a body plan in which there is only one plane of symmetry , which produces mirror-image left and right halves.

Parazoans invert during their development whereas eumetazoans do not invert at any time during their life cycle.

Parazoa have only one kind of cell during their life cycle whereas Eumetazoa have many kinds of cells throughout their life cycle.

Parazoans have mobile gametes while eumetazoans do not.

The various cell types of Parazoa do not form permanent associations into tissues during their life cycle, whereas Eumetazoa possess true, stable tissues.

Parazoans are only haploid during their life cycle, whereas eumetazoans are diploid with haploid sex cells at various stages of their life cycle.