What is the Difference Between Platyhelminthes and Aschelminthes

The main difference between Platyhelminthes and Aschelminthes is that Platyhelminthes is a phylum containing acoelomates whereas Aschelminthes is a phylum containing pseudocoelomates. Furthermore, Platyhelminths lack a non-living cuticle while Aschelminths have a non-living cuticle as a body covering.

Platyhelminthes and Aschelminthes are two phyla of true animals that belong to the division Eumatozoa. Both phyla are extremely enthusiastic as parasites.

Key Areas Covered

1. Platyhelminthes
     – Definition, Characteristics, Behavior
2. Aschelminthes
     – Definition, Characteristics, Behavior
3. What are the Similarities Between Platyhelminthes and Aschelminthes
     – Outline of Common Features
4. What is the Difference Between Platyhelminthes and Aschelminthes
     – Comparison of Key Differences

Key Terms

Acoelomates, Aschelminthes, Platyhelminthes, Pseudocoelomates

Platyhelminthes – Definition, Characteristics, Behavior

Platyhelminthes is a phylum of invertebrates composed of flatworms. It is classified into four groups based on their nature of living: Turbellaria – non-parasitic and Cestoda, Trematoda, and Monogenea – parasitic. Generally, platyhelminths are triploblastic animals with bilateral symmetry. They have a dorso-ventrally flattened body. Also, they are acoelomates as they lack a body cavity. On the other hand, the digestive system of platyhelminths is incomplete and one opening is responsible for both ingestion and egestion.

Figure 1: Platyhelminthes

Furthermore, the respiration of platyhelminths occurs through simple diffusion through the body surface. Moreover, they lack a circulatory system. The excretory system consists of Protonephridia with flame cells. On the other hand, asexual reproduction of them occurs either by regeneration or fission. Also, platyhelminths are hermaphrodites with internal fertilization.

Aschelminthes – Definition, Characteristics, Behavior

Aschelminthes is a phylum of unsegmented, triploblastic worms with a pesudocoelom. They have a cylindrical or thread-like body tapering at both ends. Their boy wall is made up of an epidermis and a muscle layer. Also, it is covered by a cuticle. As they have a body cavity, they can develop complex organ systems. In addition, although their posterior and anterior ends show a little differentiation, they show internal cephalization. On the other hand, they have a complete digestive system and the mouth occurs in the anterior end of the body.

Figure 2: Aschelminthes

Moreover, the respiration of free-living aschelminths occurs through the body surface. But, parasitic aschelminths undergo anaerobic respiration. Also, aschelminths show sexual dimorphism and are unisexual animals. They undergo internal fertilization. Although the most prominent form of aschelminths are nematodes, the whole group is made up of several phyla including Acanthocephala, Chaetognatha, Cycliophora, Gastrotricha, Kinorhyncha, Loricifera, Nematoda, Nematomorpha, Priapulida, and Rotifera.

Similarities Between Platyhelminthes and Aschelminthes

• Platyhelminthes and Aschelminthes are two phyla containing true animals of the division Eumatozoa.
• They have bilateral symmetry and are classified under the clade Bilateria.
• Moreover, they are triploblastic animals.
• They are unsegmented worms that are mostly parasitic. Some are free-living in the soil.
• In addition, they are protostomes, showing determinate and spiral cleavage.

Difference Between Platyhelminthes and Aschelminthes

Definition

Platyhelminthes refers to a phylum of worms having bilateral symmetry and a soft, usually flattened body, comprising flatworms while Aschelminthes refers to an invertebrate animal belonging to a group of phyla that are distinguished by the lack of a well-developed coelom and blood vessels. Thus, this is the main difference between Platyhelminthes and Aschelminthes.

Coelom

Another difference between Platyhelminthes and Aschelminthes is that Platyhelminthes do not contain a coelom (acoelomates) while Aschelminthes contains a pseudocoelom (pseudocoelomates).

Development of Organs

Moreover, Platyhelminthes shows a limited development of organs while Aschelminthes shows the development of complex organ systems.

Cuticle

Also, one other difference between Platyhelminthes and Aschelminthes is that the Platyhelminthes does not develop a body cover while Aschelminthes develops a non-living cuticle as a body cover.

Body

The body of Platyhelminthes is flat while the body of Aschelminthes is more cylindrical.

Also Known as

The members of Platyhelminthes are also known as flatworms while the most prominent group of Aschelminthes are roundworms.

Digestive System

There is a difference between Platyhelminthes and Aschelminthes in their digestive system as well. Platyhelminthes have an incomplete digestive system with a single opening while Aschelminthes has a complete digestive system with the mouth and anus.

Excretion

Platyhelminthes excretes through flame cells while Aschelminthes excretes through H-shape tubes.

Sex Differentiation

Furthermore, Platyhelminths are mostly hermaphrodites while Aschelminths are gonochoristic.

Locomotion

While Platyhelminths move by contracting their circular and longitudinal muscles alternatively, Aschelminths move by bending the body side to side.

Life Cycle

The life cycle is another difference between Platyhelminthes and Aschelminthes. Platyhelminths have a more complex life cycle while Aschelminths have a more predictable life cycle.

Conclusion

Platyhelminthes is a phylum of true animals with a flat body. Also, they are acoelomates. Due to the lack of a coelom, platyhelminths are less complex animals. On the other hand, Aschelminthes is a group of phyla of animals, consisting of several phyla. The most prominent phylum is Nematoda. Aschelminths are pseudocoelomates and have more complex bodies. Both Platyhelminthes and Aschelminthes are well-known for parasitic worms. However, the main difference between Platyhelminthes and Aschelminthes is the presence of a body cavity.

References:

1. “Phylum Platyhelminthes: General Characteristics and Classification.” Online Biology Notes, 9 June 2017, Available here.
2. “Phylum Aschelminthes: Characteristics, Examples with Questions & Videos.” Toppr, 26 Sept. 2018, Available Here.

Image Courtesy:

1. “Platyhelminthes (25682131783)” By LiCheng Shih – _ESF7305 (CC BY 2.0) via Commons Wikimedia   
2. “Ascaris Lumbricoides (roundworm)” By SuSanA Secretariat (CC BY 2.0) via Flickr