Definition of Pseudocoelomate, Example, Characteristics

Definition of Pseudocoelomate

A pseudocoelomate is an organism with a body cavity that is not derived from the mesoderm, as in a true coelom or body cavity. A pseudocoelomate is also known as a blastocoelomate because the body cavity is derived from the blastocoel of the cavity inside the embryo. A true coelom is lined with a peritoneum that serves to separate fluid from the body cavity. In a pseudocoelomate, bodily fluids bathe the organs and receive their nutrients and oxygen from the fluid in the cavity.

The presence of the blastocoel in the embryo is a universal condition for all metazoa. In most metazoa, the mesoderm becomes the wall of the body cavity, creating the true coelom. Some pseudocoelomates represent the primitive form of coelomates, and their ancestors never had a true coelom. Other organisms have lost the peritoneum and returned to the state of pseudocoelomate. The larval form of some coelomates begins as pseudocoelomates. A pseudocoelomate is often a small animal, which relies primarily on diffusion to deliver oxygen and nutrients to its cells. These organisms generally do not have a circulatory system or an open circulatory system that circulates a blood-like substance known as hemolymph through the body cavities of these animals. For this reason, the cavity is known as a hemocoel and the body as a hemocoeleomatous.

What are the Examples of Pseudocoelomate?

A body cavity that is surrounded by mesoderm in

next to.


Rotifers are extremely small, multicellular organisms that exist by attaching to a substrate and seeping out of water. Rotifers have a characteristic head region with hundreds of cilia, which work in unison to create jets of water that direct food particles into the mouth. Like other metazoa, rotifers have three distinct tissues or are triploblastic. The embryo of a rotifer forms a blastula, much like a human embryo. The blastocoel inside the embryo becomes a cavity that is not covered by the peritoneum. The internal organs are bathed in fluid and the oxygen diffuses directly through the outer layers of the small animal. It is the typical form of a pseudocoelomate and is beneficial for the small organism because it needs a separate circulatory system to circulate oxygen. These tiny organisms can be seen below.


Like rotifers, nematodes are small pseudocoelomates that have an altered body cavity. While the pseudocoelomate condition is sometimes considered ancestral, many organisms like nematodes have advanced body parts. Nematodes reproduce sexually, produce games, and have advanced organs to reproduce and find food, as shown in the following image. These organisms can live freely in soil or water or can be parasitic. Due to their advanced reproductive systems, these small organisms have adapted to almost any environment on the planet.

Phylum Nematoda

There are> 12,000 species found in almost all

habitats (marine, freshwater, underground, houseplants

and animals, etc …).

They are also incredibly filling. For example:

  • a m² of soil may contain >4 million nematodes • a decomposing apple may contain >90,000 nematodes of a single species


9 different edges are classified as pseudocoelomates.

  1. Nematoda
  2. Rotifera
  3. Nematomorpha
  4. Kinorhyncha
  5. Priapulida
  6. Acanthocephala
  7. Gastrotricha
  8. Entoprocta

Pseudocoelomate Characteristics

Organ level of organization

Tissues are organized for organs that are used to accomplish physiological functions

Pseudocoelomate Characteristics


3 Germ Layers 3 Tissue Layers

endoderm gastrodermis  

mesoderm -mesoderm

ectoderm- epidermis

Pseudocoelomate Characteristics

the pseudocoelom

  1. it is a closed cavity filled with fluid
  2. contains digestive, excretory, and reproductive structure
  3. the fluid inside acts as a circulatory system
  4. the internal liquid acts as a hydrostatic skeleton
  5. against which the muscles work

Bilateral Symmetry

 with anterior and posterior ends


the concentration of sensory organs in the head of the animal

Definition of Pseudocoelomate, Example, Characteristics

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