Pseudocoelomate Animals Examples

In this pseudocoelomate animals examples post we have briefly explained about pseudocoelomate animals definition, pseudocoelomates classification, contributions and examples.

Pseudocoelomates animals is an organism with a body cavity that is not generated from the mesoderm, as is the case with a true coelom. Because the bodily cavity is formed from the blastocoel, or cavity within the embryo, a pseudocoelomate is also known as a blastocoelomate.


In the nine phyla covered in this section, the original blastocoel of the embryo persists as a space, or body cavity, between the enteron and body wall. Because this cavity lacks the peritoneal lining found in true coelomates, it is referred to as a pseudocoel, and the animals that inhabit it are referred to as pseudocoelomates. Pseudocoelomates are classified as bilateral animals in the Protostomia division, but they are polyphyletic (derived independently from more than one acoelomate ancestor).


The pseudocoel is a distinct gradation in body plan compared with the solid body structure of acoelomates. The pseudocoel may be filled with fluid or may contain a gelatinous substance with some mesenchyme cells. In common with a true coelom, it presents certain adaptive potentials, although these are by no means realized in all members: (1) greater freedom of movement; (2) space for development and differentiation of digestive, excretory, and reproductive systems; (3) a simple means of circulation or distribution of materials throughout the body; (4) a storage place for waste products to be discharged to the outside by excretory ducts; and (5) a hydrostatic organ. 

Since most pseudocoelomates are quite small, the most important functions of the pseudocoel are probably in circulation and as a means to maintain a high internal hydrostatic pressure. A complete, mouth-to-anus digestive tract is found in these phyla and in all more complex phyla.


Vertebrates and more complex invertebrates have a true coelom, or peritoneal cavity, that develops in the mesoderm during embryonic development and is thus lined with a layer of mesodermal epithelium, the peritoneum.

Pseudocoelomates phyla lack a true coelom in favour of a pseudocoel. It develops from the embryonic blastocoel rather than a secondary cavity within the mesoderm. It is a non-peritoneal space between the gut and the mesodermal and ectodermal components of the body wall.

The pseudocoelomate category includes nine distinct animal groups: Rotifera, Gastrotricha, Kinorhyncha, Nematoda, Nematomorpha, Loricifera, Priapulida, Acanthocephala, and Entoprocta. Because the first five of these groups share some characteristics, they were previously classified as classes in a phylum called Aschelminthes. They differ so much, however, that their phylogenetic relationships are highly debatable, and they are now classified as separate phyla. Some people classify the five as individual phyla, while others classify them as a superphylum called Aschelminthes. The Entoprocta are sometimes combined with the Ectoprocta to form the Bryozoa (moss animals). However, because ectoprocts have a true coelom, they are usually considered a separate phylum, and the term “bryozoans” is now used to exclude entoprocts.

Pseudocoelomate Animals

Acoelomate, pseudocoelomate, and eucoelomate body plans.

According to molecular evidence, Protostomia is made up of two large groups that diverged in the Precambrian: Lophotrochozoa and Ecdysozoa. Some pseudocoelomates phyla appear to fall into each of these categories.

pseudocoelomates are a diverse group of animals, regardless of how they are classified. The majority of them are small; some are microscopic; and some are quite large. Some, like nematodes, can be found in freshwater, marine, terrestrial, and parasitic environments, while others, like Acanthocephala, are strictly parasitic. Some have distinctive features, such as acanthocephalans’ lacunar system or rotifers’ ciliated corona.

Even in such a diverse grouping, some traits are shared. All have an epidermis (often syncytial) body wall, a dermis, and muscles surrounding the pseudocoel. Except in Acanthocephala, the digestive tract is complete, and it, along with the gonads and excretory organs, is contained within the pseudocoel and bathed in perivisceral fluid. In many cases, the epidermis secretes a nonliving cuticle with some specialisations such as bristles or spines.

Eutly is a term used to describe a constant number of cells or nuclei in individuals of a species or in parts of their bodies that is shared by several groups. The longitudinal muscle layer is emphasised in the majority of them.

Pseudocoelomate Animals Examples

Pseudocoelomates any invertebrate animal with a pseudocoel, a cavity between the gut and the outer body wall derived from a persistent blastocoel, rather than a true coelom. The roundworm is an example of a Pseudocoelomates. Pseudocoelomates animals are also known as Blastocoelomate animals. Flatworms and other acoelomate animals have no body cavity at all. Semi-solid mesodermal tissues between the gut and the body wall support the organs.


Rotifers are extremely small multicellular organisms that live by adhering to a substrate and filtering water. Rotifers have a distinct head region that is covered in hundreds of cilia that work together to create streams of water that direct food debris into the mouth. Rotifers, like other metazoa, have three distinct tissues or are triploblastic.

A rotifer embryo, like a human embryo, develops into a blastula. In the embryo, the blastocoel develops into a cavity that is not covered by the peritoneum. The internal organs are submerged in liquid, and oxygen is diffused directly through the small animal’s outer layers. This is the most common type of pseudocoelomates and is advantageous for the small organism because it requires a separate circulatory system to circulate oxygen. These microscopic organisms can be seen below.

Pseudocoelomate Animals



Because nematodes have a false body cavity, they are referred to as pseudocoelomates. Pseudocoelomates animals are also known as Blastocoelomate animals. Pseudocoelmates are animals whose body cavity is pseudocoelem, i.e. the mesoderm is present as scattered pouches in between the ectoderm and endoderm rather than as a continuous layer.

Nematodes, like rotifers, are small pseudocoelomates with a modified body cavity. While the pseudocoelomates state is sometimes thought to be ancestral, many organisms have advanced body parts, such as nematodes. Nematodes reproduce sexually, produce games, and have advanced reproductive and foraging organs, as illustrated in the image below. In soil or water, these organisms can live freely or as parasites. These tiny organisms have adapted to nearly every environment on the planet due to their advanced reproductive systems.

Pseudocoelomate Animals


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