INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE METAZOA (EUMETAZOA)

SECTION DIPLOMA-BLASTICA, OR RADIATA (RADIATA)

Animals characterized by radial Symmetry. An axis can be drawn through their body, around which repeating Organs are arranged radially. This axis passes through two opposite poles of the animal's body: the oral pole, where the Mouth is located, and the opposite, aboral pole. Through the axis of Radiata, two, four, six, eight, or more planes of symmetry can be drawn, dividing the body into two similar halves.

During embryonic development, radiate animals form two germ layers (hence their name - diploblastic): the ectoderm and the 100

endoderm, from which two epithelial layers develop: the outer epidermis and the inner gastroderm. Between them lies the mesoglea, a non-cellular layer of varying degrees of development, containing isolated Cells of ectodermal or endodermal origin. Although diploblasts possess Tissues, they lack complex organs. They have no body cavity; the only cavity is the gut cavity. The Emergence of nerve, epitheliomuscular, or Muscle cells represents an evolutionary advancement.

The Radiata include two phyla.



Last update: 13/08/2026

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