Anatomy of finfish and shellfish

2.1. Organization

Unit 2 - Cell structure, tissue and body organization

2.1. Organization: kind of construction of the body
A cellular or protoplasmic level of organization: Body is not differentiated into cells. Example: Protozoa (subkingdom: Protozoa); All other animals except Protozoa come under the subkingdom: Metazoa (Body is composed of numerous cells)
Cellular level of organization: The cells of the body are more or less loose and Independent. Example: Amoeba
Tissue level of organization: In some animals, body cells form tissues. Example: Coelenterata and Ctenophora
Organ system level of organization: In most of the animals, tissues combine into organs, which, in turn, combine to form organ systems. Example: Animals like Human being, Fish, Reptiles etc.,
Germ Layers:
The fundamental cell layers laid down in an early embryo of the Metazoa are called germ layers. The Coelenterata have only two layers: Ectoderm and Endoderm. They are termed the diploblastic animals. Most other Metazoa possess three germ layers: Ectoderm, Mesoderm and Endoderm. They are known as the triploblastic animals. Example; Animals except Coelenterata