Difference Between Platyhelminthes and Aschelminthes

Key Difference – Platyhelminthes vs Aschelminthes
 

Platyhelminthes and Aschelminthes are major invertebrate phyla of the Kingdom Animalia. Platyhelminthes are acoelomates while Aschelminthes are pseudo-coelomates. This is the key difference between Platyhelminthes and Aschelminthes.

Invertebrates are defined as animals that lack a backbone. Other major phyla that include invertebrates are Cnidaria, Annelida, Arthropoda, Mollusca, and Echinodermata.

CONTENTS

1. Overview and Key Difference
2. What is Platyhelminthes
3. What is Aschelminthes
4. Similarities Between Platyhelminthes and Aschelminthes
5. Side by Side Comparison – Platyhelminthes vs Aschelminthes in Tabular Form
6. Summary

What is Platyhelminthes?

Platyhelminthes is a phylum consisting of thin, soft worms taking the shape of a leaf or similar to ribbonlike structure. Therefore, Platyhelminthes are also known as flatworms. They are found in the family planaria living in ponds while parasitic types such as flukes and tapeworms are found in animal bodies and humans.

Some characteristics are present to define the nature of Platyhelminthes. The absence of a body cavity (acoelomate), the body possessing three tissue layers (triploblastic) and the presence of a definite head while the body is symmetric to both left and right sides (bilaterally symmetrical) are unique features of Platyhelminthes.

Figure 01: The flatworm Pseudoceros dimidiatus

The phylum Platyhelminthes consist of different classes that include class Turbellaria, class Cestoda, and class Trematoda. Class Turbellaria composed of many free living organisms and some are parasitic. Trematodes are commonly known as flukes. They are parasitic flatworms with an unsegmented body. Tapeworms are referred to as Cestodes. Class Cestoda possess members with common features such as segmented ribbon like body and parasitic.

What is Aschelminthes?

Phylum Aschelminthes is defined as an obsolete phylum that contains worm like invertebrates. They are referred to as nematodes also since the major class that belongs to this phylum is class nematoda. Along with nematodes there are other classes of invertebrates such as Rotifera, Gastrotricha, Kinorhyncha, Acanthocephala and Nematomorpha.

According to present classification, each class is reclassified into separate phylum. The reason for classifying all these animals together as one group was due to the presence of a pseudocoelom. Unlike a coelom, this is a type of body cavity where there is no lining of mesoderm is present. But later it was found out that these animals had no close evolutionary links between them and therefore, each class of animals was then classified into their own phyla.

Figure 02: Aschelminthes

Rotifers and acanthocephalans have common evolutionary relationships and therefore, these two classes were placed in the same phylum. Due to all these reasons, Aschelminthes were declared as an obsolete phylum according to the modern classification system.

What are the Similarities Between Platyhelminthes and Aschelminthes?

• Both Platyhelminthes and Aschelminthes are invertebrates.
• Both lack a backbone.
• Both do not have a true coelom.
• Both Platyhelminthes and Aschelminthes are simple animals.
• Both types of animals perform all vital body functions.

What is the Difference Between Platyhelminthes and Aschelminthes?

Summary – Platyhelminthes vs Aschelminthes

Invertebrate organisms do not possess a backbone. Platyhelminthes and Aschelminthes are invertebrates who lack a backbone. Even though Platyhelminthes is considered as a phylum up to date, Aschelminthes is considered as an obsolete group of organisms. The reason for classifying all Aschelminthes together as one group was due to the presence of a pseudocoelom. Now they have been reclassified as separate phyla. Platyhelminthes is a phylum that consists of thin, soft worms taking the shape of a leaf or similar to ribbonlike structure. The phylum Platyhelminthes consist of different classes that include Class Turbellaria, Class Cestoda, and Class Trematoda. Phylum Aschelminthes is defined as an obsolete phylum that contains round worm like invertebrates. This is the difference between Aschelminthes and Platyhelminthes.

Reference:

1.“Phylum Aschelminthes: Characters and Classification | Animal Kingdom.” Biology Discussion, 12 Dec. 2016. Available here 
2.The Columbia University Press. “Platyhelminthes.” The Columbia Encyclopedia, 6th Ed, Encyclopedia.com, 2018. Available here  

Image Courtesy:

1.’Pseudoceros dimidiatus’By Richard Ling – Flickr, (CC BY-SA 2.0) via Commons Wikimedia
2.’5671047130’by Scot Nelson (Public Domain) via Flickr

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