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Coelomates vs. Pseudocoelomates: What's the Difference?

Edited by Janet White || By Harlon Moss || Updated on October 9, 2023
Coelomates have a true coelom (body cavity lined by mesoderm), while pseudocoelomates have a pseudocoelom (body cavity not entirely lined by mesoderm).

Key Differences

Coelomates represent a group of animals that have a true coelom. This true coelom is a body cavity that is fully lined with mesoderm, a layer of embryonic tissue. Pseudocoelomates, on the other hand, possess a pseudocoelom which is a body cavity that is not fully lined by mesoderm, creating a somewhat intermediate state between coelomates and acoelomates (organisms lacking a coelom).
In the development phase, coelomates display a sophisticated and advanced structure where the body cavity, or the coelom, provides room for organs and serves as a fluid-filled space, offering protection and support to those organs. Pseudocoelomates exhibit a slightly different scenario, where their body cavity is partly lined with mesoderm and partly with endoderm, offering less structural support than a true coelom.
Coelomates often demonstrate more complex body organization and structures, revealing an advanced evolutionary development with complex organ systems that are suspended within the coelom, providing not only physical support but also a medium for the circulation of nutrients and waste. Pseudocoelomates, however, may exhibit simpler organ systems and structures, reflecting their somewhat less complex evolutionary development, although there are exceptions with some pseudocoelomates having relatively complex structures and life histories.
Moreover, coelomates encompass a vast variety of animals including annelids (e.g., earthworms), mollusks, arthropods, and vertebrates, all of which share the common feature of possessing a true coelom. Conversely, pseudocoelomates include organisms such as nematodes and rotifers, which, despite lacking a true coelom, have been remarkably successful in an evolutionary sense, populating a diverse range of habitats across the globe.

Comparison Chart

Body Cavity Lining

Fully lined by mesoderm.
Partially lined with mesoderm.

Organ Support

Organs suspended in coelom, well-protected & supported
Organs not as well protected or supported.

Evolutionary Aspect

Tend to be more evolutionarily advanced.
Might be considered less advanced in some aspects.

Representative Phyla

Include Annelida, Mollusca, and Chordata.
Include Nematoda and Rotifera.

Structural Complexity

Often exhibit complex structures and organ systems.
May have simpler structures and organ systems.

Coelomates and Pseudocoelomates Definitions


Coelomates showcase advanced developmental traits, thanks to the protective and supportive nature of their coelom.
Coelomates like mollusks have complex organ systems cushioned within the coelom.


Pseudocoelomates often exhibit a simpler structural and developmental complexity compared to coelomates.
Rotifers, being pseudocoelomates, feature a basic anatomical design, managing with a partially lined body cavity.


Coelomates usually exhibit more complex and sophisticated organ systems suspended within the coelom.
The coelomates, such as arthropods, often display intricate internal anatomies.


Pseudocoelomates are organisms with a pseudocoelom, a body cavity not completely lined with mesoderm.
Nematodes are pseudocoelomates and exhibit a simple but effective body plan suitable for their parasitic and free-living lifestyles.


Coelomates encompass a wide variety of animal phyla due to the evolutionary advantage of a true coelom.
Among coelomates, vertebrates exhibit a high level of organizational complexity in their body structures.


Pseudocoelomates do not have a fully developed and enclosed circulatory system as seen in many coelomates.
Pseudocoelomates, such as nematodes, rely on their pseudocoelom to distribute nutrients and wastes due to the lack of a closed circulatory system.


Coelomates are animals possessing a true coelom, a body cavity entirely lined with mesoderm.
Earthworms, as coelomates, have a coelom that supports and protects their internal organs.


Pseudocoelomates include numerous microscopic or tiny animals that have been evolutionarily successful.
Despite their simpler body cavities, pseudocoelomates like roundworms thrive in various environments globally.


Coelomates can be found across numerous habitats, partly due to the structural and functional benefits of a coelom.
Coelomates, like annelids, utilize their coelom for distributing nutrients and removing wastes, facilitating adaptation to varied environments.


Pseudocoelomates utilize their body cavity for multiple functions, including supporting internal organs and acting as a hydrostatic skeleton.
The pseudocoelom in pseudocoelomates like rotifers also aids in maintaining their structural integrity.


Plural of coelomate


Having a pseudocoel.


An animal having a pseudocoel.


Plural of pseudocoelomate


What is a pseudocoelom?

A pseudocoelom is a body cavity partially lined with mesoderm and endoderm.

Which organisms are coelomates?

Organisms like earthworms, humans, and insects are coelomates.

Can you name an example of pseudocoelomates?

Nematodes, such as roundworms, are examples of pseudocoelomates.

What is a coelom?

A coelom is a fluid-filled body cavity completely lined with mesoderm.

Are coelomates more complex than pseudocoelomates?

Generally, yes, coelomates tend to have more complex body structures than pseudocoelomates.

Do pseudocoelomates have a circulatory system?

Pseudocoelomates typically lack a true closed circulatory system.

What is the main advantage of having a coelom?

A coelom provides support, protection to internal organs, and can facilitate more complex body structures and functions.

How does body cavity type relate to evolutionary development?

The type of body cavity (coelom, pseudocoelom, or none) is often related to evolutionary complexity and specialization in organ systems.

Do pseudocoelomates exhibit bilateral symmetry?

Yes, pseudocoelomates, like nematodes, generally exhibit bilateral symmetry.

What type of body cavity do roundworms have?

Roundworms have a pseudocoelom.

How is reproduction affected by the presence of a coelom?

A coelom allows for more complex reproductive systems and strategies in coelomates.

Are pseudocoelomates multicellular organisms?

Yes, pseudocoelomates like rotifers and nematodes are multicellular organisms.

Why are pseudocoelomates still evolutionarily successful?

Pseudocoelomates are often highly adaptable, with effective reproductive strategies, enabling success across varied habitats.

Is a coelom present in all animals?

No, not all animals have a coelom; some are acoelomates or pseudocoelomates.

How does the pseudocoelom aid pseudocoelomates?

The pseudocoelom acts as a hydrostatic skeleton and plays a role in locomotion, digestion, and the distribution of substances.

How does the coelom form in coelomates?

The coelom forms from mesodermal tissue during embryonic development.

Are all pseudocoelomates microscopic?

While many pseudocoelomates are microscopic or very small, they are not exclusively so.

Are all coelomates deuterostomes?

No, not all coelomates are deuterostomes; for instance, arthropods and mollusks are protostomes.

Can you name a marine example of coelomates?

An example of marine coelomates is octopuses.

What roles does the coelom play in animal locomotion?

In many animals, the coelom acts as a hydrostatic skeleton, facilitating movement through fluid pressure.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.

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