Acoelomate
- Acoelomate
An **acoelomate** is an organism that lacks a coelom, or body cavity, between the digestive tract and the outer body wall. This characteristic is a significant aspect of the body plan of certain invertebrates, particularly within the phylum Platyhelminthes, which includes flatworms. Acoelomates are contrasted with coelomates, which have a true coelom, and pseudocoelomates, which have a body cavity that is not entirely lined with mesoderm.
Characteristics[edit | edit source]
Acoelomates are defined by their solid body structure. The space between the digestive tract and the body wall is filled with mesenchyme, a type of connective tissue. This lack of a body cavity affects the organism's physiology and development in several ways:
- **Lack of Circulatory System**: Due to the absence of a coelom, acoelomates do not have a circulatory system. Nutrients and waste products diffuse directly through the tissues.
- **Simple Body Plan**: Acoelomates typically have a simple body plan with three primary tissue layers: the ectoderm, mesoderm, and endoderm.
- **Limited Size and Complexity**: The absence of a coelom limits the size and complexity of acoelomate organisms, as the solid body structure restricts the development of complex organ systems.
Examples[edit | edit source]
The most well-known examples of acoelomates are the flatworms, which belong to the phylum Platyhelminthes. This group includes:
- **Planarians**: Free-living flatworms that are often used in scientific research due to their regenerative abilities.
- **Flukes**: Parasitic flatworms that can infect various hosts, including humans.
- **Tapeworms**: Parasitic flatworms that live in the digestive tracts of vertebrates.
Evolutionary Significance[edit | edit source]
The acoelomate condition is considered a primitive trait in the evolution of bilaterian animals. It is believed that the acoelomate body plan represents an early stage in the evolution of more complex body plans, such as those seen in coelomates and pseudocoelomates. The study of acoelomates provides insights into the evolutionary transitions that led to the diversity of body plans observed in the animal kingdom today.
Also see[edit | edit source]
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