- Body-cells are loosely arranged in two layers, which are separated by Mesenchyme.
- Numerous Ostia are present throughout the body and a large opening Osculum is found on the upper end.
- Canalsystem is present, through which water flows throughout the body supplying food and O2.
- Endoskeleton is made up of calcareous and siliceous spicules, and spongin fibres.
- Several Chonaocyte-lined spaces are present.
Examples: Sycon, Spongilla