What Is Pseudocoelomate: Definition And Examples?


Pseudocoelomate Definition

A pseudocoelomat is an organism with a body cavity that does not originate from the mesoderm like a true coelom or body cavity. A pseudocoelomate is also known as a blastocoelomate because the body cavity is derived from the blastocoel, or cavity in the embryo.

What is Pseudocoelomate?

A pseudocoelomat is a group of organisms with a three-layered body that has a fluid-filled body cavity not derived from the mesoderm as is present in the true coelom body cavity. However, the body cavity is derived from the blastocoel, also known as the blastocoelomate.

A perivisceral cavity, which is not a true coelom, is present in pseudocoelomates. A true coelom lined with the peritoneum that separates the fluid from the body cavity. The organs get their nutrients and oxygen from the fluid in the body cavity.

It originates from the embryonic blastocoel rather than the secondary cavity within the mesoderm. Blastocoel is a space between the intestine and the mesodermal and ectodermal components of the body wall, it is not lined with peritoneum.

The presence of the blastocoel in the embryo is a universal condition in all metazoans. In most metazoans, the mesoderm becomes the lining of the body cavity, giving rise to the true coelom. Some of the pseudocoelomates represent the primitive form of the coelomates, and their ancestors have no true coelom. Some of the other organisms have lost the peritoneum and reverted to the pseudocoelomate state.

Some of the larval forms of coelomates are started as pseudocoelomates. A pseudocoelomate is often a small animal that relies primarily on diffusion to distribute oxygen and nutrients throughout its cell.


They don’t have a circulatory system, but they do have an open circulatory system known as hemolymph, which circulates a blood-like substance in the body cavities of these animals. For this reason, the cavity is called the hemocoel and the organism is called the homocoelomat.

Examples of Pseudocoelomate

Pseudocoelomat Describes any invertebrate whose body cavity is a pseudocoel, a cavity between the gut and the outer body wall derived from a persistent blastocoel rather than a true coelom.

An example of a pseudocoelomate is a roundworm. Pseudocoelomate animals are also known as blastocoelomates. Like flatworms, acoelomate animals have no body cavity at all. Semi-rigid mesodermal tissue between the gut and body wall holds your organs in place.


Rotifers are extremely small multicellular organisms that exist by attaching themselves to a substrate and filtering themselves out of water. Rotifers have a distinctive head region with hundreds of cilia that work together to create streams of water that channel food debris into the mouth. Like other metazoans, the rotifers have three distinct tissues or are triploblastic.

This is the typical form of a pseudocoelomate and is beneficial for the small organism as it needs a separate circulatory system to circulate oxygen. These tiny organisms can be seen below.

The embryo of a rotifer forms a blastula, similar to a human embryo. The blastocoel in the embryo develops into a cavity that is not covered by the peritoneum. The internal organs are immersed in liquid and oxygen is diffused directly through the small animal’s outer layers.

This is the typical form of a pseudocoelomate and is beneficial to the small organism as it requires a separate circulatory system to circulate oxygen.


Nematodes have a false body cavity and are therefore called pseudocoelomatous. Like rotifers, nematodes are small pseudocoelomates with a modified body cavity. While the pseudocoelomates state is sometimes thought to be an ancestor, many organisms, such as the nematodes, have an advanced body part.

Nematodes reproduce sexually, produce games, and have advanced reproductive and foraging organs as shown in the image below. These organisms can live freely or parasitize in soil or water. Because of their advanced reproductive systems, these tiny organisms have adapted to almost any environment on the planet.

Nematodes reproduce sexually

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