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
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.
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.
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
Definition
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.
Significance
Setae are bristles secreted from the distal ends of parapodia, while parapodia are lateral extensions supported by chitin.
Importance
Setae differ in structure and function among species, while parapodia contain bundles of setae.
Occurrence
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.
Conclusion
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.
References:
- Encyclopædia Britannica, inc. (n.d.). Locomotion. Encyclopædia Britannica.
Image Courtesy:
- “Isonychia Foreleg” By Erin Hayes-Pontius – Own Work (CC BY SA 3.0) via Commons Wikimedia
- “L oculatus para wscale” By Sus barbatus – Own Work (CC-BY SA 4.0) via Commons Wikimedia
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