Question

In some animals, the body cavity is not lined by mesoderm. Instead the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called (a) Eucoelom (b) Pseudocoelom (c) Acoelom (d) Any of the above

Short answer

The body cavity where the mesoderm is present as scattered pouches in between the ectoderm and endoderm is known as a Pseudocoelom.

Step-by-step solution

Understand the Nature of Different Body Cavities

The first step is to comprehend the distinctions between the three types of body cavities mentioned in the exercise. A body cavity filled entirely with mesoderm is an Eucoelom. In an Acoelom, there is no body cavity, and the space between the gut and the body wall is filled solidly with tissue (mainly muscle). Lastly, a Pseudocoelom refers to a cavity that is not entirely lined with mesoderm, but the mesoderm is present as isolated pouches in between the ectoderm and endoderm.

Connect the Provided Information with the Concepts

The structure provided in this question states that the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Comparing this information to the definitions of different body cavities, this structure is most aligned with the definition of a Pseudocoelom.

Key concepts

Eucoelom

A eucoelom, also known as a true coelom, is a type of body cavity characterized by being fully lined with mesoderm on all surfaces. This mesodermal lining allows for well-organized and compartmentalized body systems. Within a eucoelom, organs are encased and supported in a manner that aids their function and protection. This structure not only offers stability but also allows for more complex physiological processes.
Organisms possessing a eucoelom can develop more intricate body systems, such as a well-defined digestive tract and advanced organ systems. This is because the mesodermal lining allows the inner organs to move independently from the muscular wall and enables the formation of blood vessels, facilitating nutrient and waste exchange.
Key points about eucoeloms include:

• Full mesodermal lining.
• Complex development of organ systems.
• Common in many advanced multicellular animals, including most vertebrates.

Acoelom

In contrast to a eucoelom, an acoelom represents the simplest form regarding body cavity. Animals with an acoelom, known as acoelomates, have no body cavity between their digestive tract and the outer body wall. Instead, these regions are filled entirely with solid tissue, most often muscle.
This lack of a cavity means that acoelomates generally possess less complex organ systems compared to those with a true coelom or a pseudocoelom. Without a defined cavity, there's limited space for organs to develop independently, which impacts the overall complexity and efficiency of the circulatory and respiratory systems.
Some key characteristics of acoelomates include:

• No body cavity; space is filled with tissue.
• Simpler body structure.
• Often found in simpler organisms, such as flatworms.

Body Cavity

The concept of a body cavity is foundational in understanding animal anatomy and development. Body cavities are crucial as they provide a space for the development and functioning of internal organs. They dictate how organs are organized, maintained, and how they perform their functions within various animal groups.
A body cavity serves multiple functions, such as allowing organ growth and movement, housing organ systems, and facilitating the distribution of nutrients and waste materials through specialized tissues like mesoderm.
In broader terms, body cavities are typically classified into:

• Eucoelom: Where the cavity is fully lined with mesoderm, promoting complex systems.
• Pseudocoelom: Partially lined with mesoderm; simpler than eucoelomate systems, but more developed than acoelomate ones.
• Acoelom: Lacks a cavity completely; herein, internal space is filled with solid tissue.

Each type of body cavity has different implications for the organism's sophistication and functioning, influencing evolutionary adaptations and biodiversity across species.