1. Multicellular animals can be classified based on their level of organization, symmetry, presence of body cavities, digestive system structure, and segmentation.
2. Key characteristics include whether they have tissues, bilateral or radial symmetry, acoelomate, pseudocoelomate, or eucoelomate body plans, and incomplete or complete digestive tracts.
3. The animal kingdom is divided into several phyla including porifera, cnidaria, platyhelminthes, nematoda, mollusca, annelida, arthropoda, and chordata based on these structural features.
7. 3.
Body cavity or coelom)
3.1
No body cavity or
acoelom) Body covering
(from ectoderm)
Acoelomate: Acoelomates such as Tissue-
filled region
flatworms lack a body cavity
(from
between the digestive tract and outer mesoderm)
body wall.
Digestive tract
(from endoderm)
9. 3.3 Eucoelom
or coelom) Body covering
(from ectoderm)
Coelom
Coelomate. Coelomates such as
annelids have a true coelom, Tissue layer
a body cavity completely lining coelom
lined by tissue derived from and suspending
mesoderm. internal organs
(from mesoderm)
Digestive tract
(from endoderm)
Figure 32.8a
10. 4.
4.1
(Protostomia)
4.2 Anus Mouth
(Deuterostomia) Digestive tube
Mouth Anus
Mouth develops Anus develops
from blastopore from blastopore