Difference Between Coelomate and Acoelomate

The Difference between Coelomate and Acoelomate is the presence or absence of a coelom, a fluid-filled body cavity that encloses internal organs. Coelomates are organisms that have a coelom, while Acoelomates do not. This primary difference in the body plan of organisms also gives rise to many structural and functional differences. In this article, we will read about the difference between Coelomate and Acoelomate, coelomates and acoelomates, and their examples.

Difference between Coelomate and Acoelomate

The main differences between Coelomates and Acoelomates can be summarized in the following points:

Characteristic	Coelomates	Acoelomates
Coelom	Fluid-filled body cavity or coelom present.	Fluid-filled body cavity or coelom absent.
Mesoderm	Mesoderm present forms the outer layer of coelom	Mesoderm may be missing or not involved in coelom formation
No of Body Layers	Triploblastic	Diploblastic
Body Structure	More complex with distinct body cavities	Simpler, with organs directly embedded in the body’s tissue
Body Support	The mesoderm provides support to the body.	The absence of mesoderm causes a lack of body support.
Organ Movement	Organs have more freedom of movement within the coelom	Organs have limited movement as they are embedded in the body tissue
Protection of Organs	Organs are protected within the coelom	Limited protection for organs
Internal Organs	Usually, they have highly developed organ systems with their cavities, like digestive, circulatory, and nervous systems.	Usually, they have less developed organ systems.
Examples in Animal Kingdom	Vertebrates (mammals, birds, fish) and invertebrates (arthropods, mollusks)	Flatworms (e.g., planarians) and other simpler invertebrates
Energy Requirements	Higher energy is required for the development of the coelom	Lower energy is required for embryonic development
History of Evolution	Generally more evolutionarily advanced	Often considered more primitive in evolution
Body Symmetry	Bilateral symmetry is common	Radial symmetry is more common
Function of Body Cavity	Coelom serves as a hydrostatic skeleton, aiding in movement and support.	Lack of coelom may result in a more rigid body structure.
Method of Reproduction	Diverse reproductive strategies, including internal fertilization.	Reproductive strategies may be simpler, often involving external fertilization.

What is Coelomate?

Coelomates are animals with a coelom, a fluid-filled cavity between the body wall and the gut. This group of animals is characterized by the presence of mesoderm along with an endoderm and ectoderm; thus, they are also called triploblastic. The presence of coelom enables these animals to have complex body division that helps in movement. Also, they have highly developed internal organs protected by the coelom, and the coelomic fluids act as a hydrostatic skeleton that absorbs any external shock.

Alo Read: Diploblastic And Triploblastic Organization

Examples of Coelomates

Well-known examples of coelomates include organisms from both vertebrate and invertebrate species. These include:

• Annelids: Annelids refer to a class of triploblastic, coelomate organisms commonly called segmented worms. Although they are invertebrates, they have organ system level organization with circulatory and digestive systems.
• Mollusks: Mollusks belong to the Phylum Mollusca, which comprises soft-bodied animals usually covered by a shell. These are also invertebrates, triploblastic and coelomate organisms.
• Arthropods: Arthropods are eucoelomates, triploblastic, and invertebrate organisms with a cutaneous exoskeleton and segmented appendages.
• Chordates: Chordates are organisms that possess a notochord, a dorsal nerve chord, and pharyngeal gill slits. These are advanced organisms that have true coelom and are triploblastic. Examples include reptiles, apes, mammals, etc.

What is Acoelomate?

Acoelomates are organisms that lack the coelom. These organisms do not have a mesoderm and only have two body layers, the ectoderm, and endoderm, making them diploblastic. These organisms have a more primitive body structure with simple internal organs. Lack of coelom also leads to simple movement. Invertebrates like flatworms (e.g., planarians) are the best examples.

Examples of Acoelomates

Examples of acoelomate organisms are:

• Flatworms (Platyhelminthes): Flatworms, as the name suggests, have flattened body surfaces and only two germ layers, ectoderm and endoderm, with no coelomic cavity or fluid for example, liver flukes.
• Nemertea (ribbon worms): These are bilaterally symmetrical flattened worms with unsegmented bodies with only two germ layers. They do not have a mesoderm and lack a coelom as well.
• Nematodes (Roundworms): Roundworms are psuedocoelomates. They do not have a true coelom but possess a cylindrical unsegmented body. Examples include Ascaris lumbricoides, hookworm, etc.
• Other lower organisms like cnidarians and poriferans are also classified as acoelomates.

Function of Coelom in Coelomate and Acoelomate

The function of the coelom in coelomates and acoelomates can be summarized as:

• It helps maintain the body shape of an organism.
• It provides flexibility to the body.
• It keeps the internal organs in position while allowing space to grow and move as required.
• The coelomic fluid acts as a hydraulic shock absorber, preventing internal organ damage.
• The coelomic fluid also serves as a medium for the exchange of nutrients and gases along with excretory materials.
• The coelomic cavity is also the site of the maturation of gametes during embryonic development.

Conclusion – Difference between Coelomate and Acoelomate

In conclusion, the existence or lack of a coelom, a cavity in the body filled with fluid, is the primary difference between coelomates and acoelomates. Acoelomates lack this chamber, with their organs embedded straight into the solid tissue, whereas coelomates have a real coelom that allows for the growth and movement of their organs. This structural divergence has major ramifications for the complexity and functionality of the contrasting body designs in these two animal groups.

FAQ’s – Difference between Coelomate and Acoelomate

What is the main Difference between Body Cavity and Coelom?

The body cavity can be any cavity in the body of any organism, while coelom is if the mesoderm lines the cavity.

Are Echinodermata Coelomate or Acoelomate?

Echinodermata is characterized by a true coelom derived from the mesoderm. Hence, echinodermata are coelomates.

What are the Three Types of Coelom?

There are two main types of coelom: the schizocoelom and the enterocoelom. Some animals are also called psuedocoelomates due to the presence of a body cavity that lined by mesoderm.

What is the Difference between Pseudocoelom and Coelom?

A true coelom is derived and lined by the mesoderm, but a psuedocoelom is not fully lined by the mesoderm.

Are Humans Psuedocoelomates or Coelomates?

Humans and vertebrates have a true coelom. Thus, they are coelomates. In humans, the coelom is derived from the gut (primitive archenteron); therefore, they have an enterocoelus coelom.

Is Porifera an Acoelomate?

Yes, Porifera (sponges) are acoelomates, lacking a true body cavity and defined tissue layers or organs. Their simple body plan consists of specialized cells organized into a porous structure.

What is an example of a coelomate and an acoelomate?

Acoelomates encompass organisms in the phylum Platyhelminthes, commonly known as flatworms.