A triploblastic organism
which does not have an internal body cavity
other than the gut
. The area between the gut and the organism's outer body wall is completely filled with tissue
derived from the mesoderm
. The term is used to classify multicellular animal
s by developmental
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.