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How are animal phyla distinguished by body plans?
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Animal
The fallow deer (Dama dama) has been introduced in many areas ever since the Neolithic Period.
Animal phyla are distinguished by several fundamental morphological characteristics that define their body plans. These features occur in unique combinations for each phylum, serving as a basis for classification.1
Key Distinguishing Features
- Symmetry: Most animals exhibit bilateral symmetry, where a single plane divides the body into equivalent halves. Other patterns include radial symmetry, spherical symmetry, and asymmetry.23
- Cellular Differentiation and Germ Layers: Animals are categorized by whether they possess two embryonic germ layers (ectoderm and endoderm) or three, including the mesoderm.1
- Body Cavity: Bilateral animals are often classified by their internal cavity structure:
- Acoelomates: Lack a fluid-filled body cavity.4
- Pseudocoelomates: Possess a cavity between the endoderm and mesoderm.4
- Coelomates: Feature a true coelom within the mesoderm.41
- Segmentation: Some phyla are characterized by segmentation, where the body consists of a row of repeating units.1
- Developmental Patterns: Coelomate phyla are further divided into protostomes and deuterostomes based on differences in early embryonic cleavage, the fate of the blastopore, and the method of coelom formation.5