Development in Different Animal Taxa:
As discussed in a previous chapter, animals can be divided into three major groups according to how they develop. In the
sponges (
Phylum Porifera) and similar animals, there is no embryonic development at all. These animals have no true tissues, and it’s not an exaggeration to say that they’re basically just clumps of cells. These animals are sometimes referred to as the
Parazoa (“beside-animals”), indicating that they split off from the main line of animal evolution (the Eumetazoans) very early.
Development in a sponge: There is no gastrulation and, therefore, no embryonic tissues form. As
a result, the adult animal is basically a clump of largely undifferentiated cells with no true tissues or organs.
Development in Different Animal Taxa
Linear Mode
