What is the Difference Between Setae and Parapodia

The main difference between setae and parapodia is that setae are movable bristles in annelids, whereas parapodia are fleshy outgrowths on each segment of the annelid.

Setae and parapodia are two external structures occurring in the segmented body of annelids. They are essential for the locomotion of annelids. 

Key Areas Covered

1. What are Setae
– Definition, Facts, Features
2. What are Parapodia
– Definition, Facts, Features
3. Similarities Between Setae and Parapodia
– Outline of Common Features
4. Difference Between Setae and Parapodia
– Comparison of Key Differences
5. FAQ: Setae and Parapodia
– Answers to frequently asked questions

Key Terms  

Antibiosis, Setae

Difference Between Setae and Parapodia - Comparison Summary

What are Setae

Setae are various chitinous structures occurring in the segments of annelids. They are essential to attach the annelid to the surface. Also, they serve as bristles necessary for the organism’s locomotion. Epidermal cells secrete setae, consisting of a basal portion within a follicle. Additionally, a seta consists of a shaft projection from the follicle.

Differentiate Setae and Parapodia

Figure 1: Setae on the Foreleg of a Mayfly 

Earthworm’s setae reveal their function in annelids. They do not have parapodia or other appendages for locomotion, while setae are their primary locomotion feature. These setae extend from the body while anchoring to the contracting body muscles. They also attach to the surface. Circular muscles attached to the setae determine the forward movement of the earthworm. Meanwhile, specific muscles prevent the backward movement. 

Furthermore, setae also occur in vertebrates. Also, fungal, plant, and synthetic setae occur in different organisms.

What is Parapodia

Parapodia are unjointed, lateral outgrowths occurring in annelids. Also, they are essential for respiration and swimming. Importantly, they appear in tapeworms. Free-moving polychaetes undergo locomotion by circular, longitudinal, and parapodial muscles. Coelomic fluid also aids in this process. For example, the sweeping movement of parapodia is responsible for the slow movement of the worm called Nereis. Further, it gives a contractual force. Further, aciculae or needle-like processes project beyond the parapodium, aiding the crawling process.

Setae vs Parapodia

Figure 2: Lepidonotus oculatus Specimen, with a Microscope Image of One of Its Parapodia  

Moreover, parapodia do not occur in burrowing polychaetes and tube-dwelling, sedentary forms. 

Similarities Between Setae and Parapodia

  • Setae and parapodia are two external structures that occur in annelids.
  • They are essential in locomotion.
  • Also, they are important in digging.

Difference Between Setae and Parapodia


Setae refers to a stiff structure resembling a hair or a bristle, especially in an invertebrate. In contrast, parapodia refer to each of several paired muscular bristle-bearing appendages used in locomotion, sensation, or respiration.


Setae are bristles secreted from the distal ends of parapodia, while parapodia are lateral extensions supported by chitin.


Setae differ in structure and function among species, while parapodia contain bundles of setae.


Setae occur in earthworms, while parapodia occur in tapeworms.

FAQ: Setae and Parapodia

What are the functions of the parapodia and setae?

Respiration and swimming are the two functions of parapodia. However, defense, movement, and filter feeding are the functions of setae.   

What are parapodia in earthworms?

Parapodia are lateral outgrowths that predominantly occur in annelids. They are essential for creeping and swimming. 

What annelids have many setae and parapodia?

A worm called polychaete has many setae projecting off from the body. They are padded-like feet used for the movement of polychaete. 


In brief, setae and parapodia are two external structures of annelids. They are essential for locomotion and respiration. Setae are bristles occurring in the distal ends of parapodia. They have different structures varying among species. In comparison, parapodia are external structures supported by chitin. Also, they contain bundles of setae. Therefore, the main difference between setae and parapodia is their structure and function.  

  1. Encyclopædia Britannica, inc. (n.d.). Locomotion. Encyclopædia Britannica. 
Image Courtesy:
  1. Isonychia Foreleg” By Erin Hayes-Pontius – Own Work (CC BY SA 3.0) via Commons Wikimedia
  2. L oculatus para wscale” By Sus barbatus – Own Work (CC-BY SA 4.0) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology and Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things. She has a keen interest in writing articles regarding science.

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