Platyhelminthes vs. Nematoda — What's the Difference?
By Tayyaba Rehman & Urooj Arif — Updated on May 15, 2024
Platyhelminthes (flatworms) are mostly parasitic, flat-bodied invertebrates, lacking a body cavity, while Nematoda (roundworms) are cylindrical, with a distinct digestive tube and a body cavity.
Difference Between Platyhelminthes and Nematoda
Table of Contents
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Key Differences
Platyhelminthes, or flatworms, exhibit a dorsoventrally flattened body, which aids in living in their mostly aquatic or host environments. In contrast, Nematoda, known as roundworms, have a cylindrical body shape that is more suited to soil or tissue environments.
Platyhelminthes lack a true body cavity (acoelomate), which impacts their organ development and limits them to simpler bodily functions. On the other hand, Nematoda possess a pseudocoelom, a fluid-filled body cavity that better supports their organs and allows for more complex physiological processes.
The nervous system of Platyhelminthes is relatively primitive, consisting of a simple ladder-like structure, suitable for their less complex movements and behaviors. Nematoda have a more developed nervous system with a dorsal and ventral nerve cord, facilitating more advanced sensory and motor functions.
Platyhelminthes typically absorb nutrients directly through their skin, due to the absence of a digestive tract in many species. Conversely, Nematoda have a complete digestive system with a distinct mouth and anus, allowing for more efficient digestion and nutrient absorption.
Comparison Chart
Body Shape
Flat and ribbon-like
Cylindrical and thread-like
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Body Cavity
Acoelomate (no body cavity)
Pseudocoelomate (false body cavity)
Digestive System
Incomplete or absent
Complete (mouth to anus)
Nervous System
Simple, ladder-like
More complex with dorsal and ventral cords
Compare with Definitions
Platyhelminthes
Invertebrates with a flat, soft body.
A tapeworm, a type of Platyhelminthes, can cause serious health issues if ingested.
Nematoda
A tough outer layer that protects the body.
Nematoda have a cuticle that sheds during growth, a process known as molting.
Platyhelminthes
Living in or on another organism and benefiting at the host's expense.
Schistosomes, a group of Platyhelminthes, are notorious for causing schistosomiasis.
Nematoda
Worms with a long, cylindrical body that is tapered at both ends.
Nematodes can be found in diverse environments from soil to aquatic habitats.
Platyhelminthes
An animal lacking a fluid-filled body cavity.
Platyhelminthes are acoelomates, which influences their shape and physiology.
Nematoda
Having distinct male and female individuals.
Unlike many Platyhelminthes, Nematoda are typically dioecious, promoting genetic diversity.
Platyhelminthes
Organisms that possess both male and female reproductive organs.
Many Platyhelminthes species can self-fertilize due to being hermaphroditic.
Nematoda
Not dependent on another organism for life.
Many Nematoda are free-living, thriving independently in soil.
Platyhelminthes
Having a life cycle that involves multiple hosts.
Some Platyhelminthes have digenetic life cycles, complicating efforts to control their spread.
Nematoda
An animal with a body cavity that is not derived from the mesoderm.
As pseudocoelomates, Nematoda have a body cavity that aids in their nutrient distribution.
Platyhelminthes
Flatworms
Nematoda
A phylum of worms, having a long, round, and generally smooth body; the roundworms. They are mostly parasites, in plants and animals, but some are free-living in soil or water. Also called Nematoidea.
Nematoda
Unsegmented worms: roundworms; threadworms; eelworms
Common Curiosities
What primarily distinguishes Platyhelminthes from Nematoda in terms of body structure?
Platyhelminthes are flat and lack a body cavity, whereas Nematoda are cylindrical with a pseudocoelom.
Can both Platyhelminthes and Nematoda be found in aquatic environments?
Yes, both can inhabit aquatic environments, but Platyhelminthes are more commonly associated with either aquatic or host environments, while Nematoda are typically found in soil or as parasites.
How do Platyhelminthes and Nematoda differ in their nervous systems?
Platyhelminthes have a simpler, ladder-like nervous system, while Nematoda possess a more complex system with nerve cords.
Are all Platyhelminthes parasitic?
Not all; while many are parasitic, such as tapeworms and flukes, there are also many free-living species, particularly in marine and freshwater environments.
Do Nematoda have any beneficial applications for humans?
Yes, certain nematodes are used in biological pest control to manage soil-borne pests, offering an environmentally friendly alternative to chemical pesticides.
What is the significance of the digestive system differences between the two groups?
The complete digestive system of Nematoda allows for more efficient nutrient processing compared to the often absent or incomplete system in Platyhelminthes.
What roles do Nematoda play in the ecosystem?
Nematoda are crucial for soil health, aiding in the decomposition process and nutrient cycling, though some species can be harmful as plant or animal parasites.
What is the impact of Platyhelminthes on human health?
Many Platyhelminthes, especially parasitic species like tapeworms and liver flukes, pose significant health risks to humans, causing various diseases.
Why do Platyhelminthes not require a complex circulatory system?
Due to their flat bodies, Platyhelminthes can diffuse nutrients and oxygen directly through their bodies, eliminating the need for a complex circulatory system.
How do the reproductive systems of Nematoda enhance their survival in diverse environments?
The sexual reproduction system in Nematoda allows for genetic diversity, which is crucial for adaptability and survival in varied environmental conditions.
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Written by
Tayyaba RehmanTayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
Co-written by
Urooj ArifUrooj is a skilled content writer at Ask Difference, known for her exceptional ability to simplify complex topics into engaging and informative content. With a passion for research and a flair for clear, concise writing, she consistently delivers articles that resonate with our diverse audience.
