Main Difference – Flatworms vs Roundworms
Flatworms and roundworms are two types of worms with many differences in their body. Flatworms belong to the phylum Platyhelminthes while roundworms belong to the phylum Nematoda. The main difference between flatworms and roundworms is that flatworms consist of a dorso-ventrally flattened body whereas roundworms consist of a cylindrical body tapered to a fine point at each end. Both roundworms and tapeworms are triploblastic animals with bilateral symmetry. They are protostomes, exhibiting the spiral, determinate cleavage.
Key Areas Covered
1. What is a Flatworm
– Definition, Body structure, Pathology
2. What is a Roundworms
– Definition, Body Structure, Pathology
3. What are the Similarities Between Flatworm and Roundworm
– Outline of Common Features
4. What is the Difference Between Flatworm and Roundworm
– Comparison of Key Difference
Key Terms: Cestoda, Flatworm, Intestinal Parasites, Nematoda, Platyhelminthes, Roundworm, Sucking Mouthparts
What are Flatworms
Flatworms refer to a phylum of invertebrates, comprising of a dorso-ventrally flattened body. Around 20,000 flatworm species can be found on earth. Most flatworms are parasitic. Some are free-living in seawater or fresh water. Flatworms are triploblastic animals with bilateral symmetry. Their body is dorso-ventrally flattened. They are acoelomates since they lack a body cavity. Flatworms have an incomplete digestive system. They also have a gastrovascular cavity, which serves as the stomach. A single opening serves as both mouth and anus. A flatworm is shown in figure 1.
Figure 1: A Flatworm
Respiration of flatworms occurs by simple diffusion through the body surface. The excretory system of flatworms consists of protonephridia with Flame cells. The gliding type locomotion of flatworms occurs through cilia. Asexual reproduction of flatworms occurs either by regeneration or fission. Flatworms are hermaphrodites with internal fertilization. Turbellaria, Trematoda, and Cestoda are the three classes of flatworms.
What are Roundworms
Roundworms refer to a phylum of invertebrates with cylindrical bodies. Around 15,000 species of roundworms have been identified in the world. Since roundworms consist of a full-fledged body cavity, they are classified as pseudocoelomates. Roundworms consist of a hard outer covering called cuticle in their epidermis. The body surface of roundworms consists of ridges, warts, and rings. The head of the roundworms possesses sensory bristles and solid shields. Roundworms consist of a complete digestive system. The mouth consists of a sharp stylet used for sucking liquid. The thrashing motion of roundworms occurs through longitudinal muscles. A roundworm is shown in figure 2.
Figure 2: A Roundworm
Roundworms consist of a life cycle with seven stages: egg, four larval stages, and two adult stages. Some nematodes are hermaphrodites, and others are dioecious. Hermaphrodites reproduce through self-fertilization. Separate male and female individuals reproduce through copulation. Filaria worms (cause elephantiasis), Ascaris (cause ascariasis), hookworms (infestation for a long time causes anemia and helminthiasis), Trichinella (cause trichinosis), and pinworms (infest the large intestine) are examples of roundworms.
Similarities Between Flatworms and Roundworms
- Both flatworms and roundworms belong to the kingdom Animalia.
- Some flatworms and roundworms are free-living, and some are parasitic.
- Both flatworms and roundworms are unsegmented worms.
- Both flatworms and roundworms are multicellular, mobile, invertebrate animals.
- Both flatworms and roundworms are heterotrophs.
- Both flatworms and roundworms show bilateral symmetry.
- Both flatworms and roundworms show organ level organization.
- Both flatworms and roundworms are triploblastic animals.
- Both flatworms and roundworms are protostomes.
- Both flatworms and roundworms show spiral, determinate cleavage.
Difference Between Flatworms and Roundworms
Definition
Flatworms: Flatworms refers to a phylum of invertebrates, comprising of a dorso-ventrally flattened body.
Roundworms: Roundworms refers to a phylum of invertebrates with cylindrical bodies.
Phyla
Flatworms: Flatworms belong to the phylum Platyhelminthes.
Roundworms: Roundworms belong to the phylum Nematoda.
Classification
Flatworms: Turbellaria, Trematoda, and Cestoda are the three classes of Platyhelminthes.
Roundworms: Roundworms and Secernentea are the two classes of Nematoda.
Coelom
Flatworms: Flatworms are acoelomate animals.
Roundworms: Roundworms are pseudocoelomate animals.
Type of Protostomes
Flatworms: Flatworms belong to the superfamily Lophotrochozoa.
Roundworms: Roundworms belong to the superfamily Ecdysozoa.
Size
Flatworms: The size of the tapeworm may vary from 1 mm to 15 m.
Roundworms: Roundworm in humans may grow up to 35 cm.
Body Structure
Flatworms: Flatworms consist of a flat body.
Roundworms: Roundworms consist of a cylindrical body tapered to a fine point at each end.
Outer Covering
Flatworms: Flatworms lack a cuticle. The body of Platyhelminthes often contains cilia.
Roundworms: Roundworms consist of a hard outer covering called cuticle.
Digestive System
Flatworms: Flatworms consist of an incomplete digestive system.
Roundworms: Roundworms consist of a complete digestive system.
Locomotion
Flatworms: Flatworms exhibit a thrashing motion.
Roundworms: Roundworms exhibit a gliding locomotion.
Reproduction
Flatworms: Flatworms are unisexual animals that reproduce through copulation.
Roundworms: Roundworms are hermaphrodites that reproduce through cross-fertilization.
Transmission
Flatworms: Flatworms are transmitted by consuming infected fleas.
Roundworms: Roundworm can be transmitted by infected fecal matter or consuming animal tissue with worm larva.
Lives in
Flatworms: Flatworms live in the intestine.
Roundworms: Roundworms live in the small intestine.
Diagnosis
Flatworms: Flatworm segments can be identified in the feces. Diarrhea and vomiting may occur in large infections.
Roundworms: Roundworms can be diagnosed by the fecal flotation exam. Adult roundworms may reveal through the vomit.
Pathology
Flatworms: Flatworm infections may cause weight loss and tiredness.
Roundworms: Roundworm may cause large infections in lungs.
Diseases
Flatworms: Schistosomiasis, lung flukes, and liver flukes are the diseases caused by flatworms.
Roundworms: Ascariasis, hookworm disease, and trichuriasis are the diseases caused by roundworms.
Conclusion
Flatworms and roundworms are two types of worms that live either free in the environment or live as parasites in the intestine of animals. Flatworms belong to the phylum Platyhelminthes. They consist of a dorso-ventrally flattened body. Roundworms belong to the phylum Nematoda. They consist of a cylindrical body. Thus, the main difference between flatworms and roundworm is the structure of the body of each type of worm.
References:
1. Smyth, James Desmond. “Flatworm.” Encyclopædia Britannica, inc., 6 Feb. 2014, Available here.
2. Introduction to the Platyhelminthes, Available here.
3. “Roundworms.” University of Maryland Medical Center, Available here.
4. “Roundworm.” NHS Choices, NHS, Available here.
Image Courtesy:
1. “Hookworm filariform A” By Fernandolive – Own work (Public Domain) via Commons Wikimedia
2. “New Zealand flatworm” by S. Rae (CC BY 2.0) via Flickr
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