The key difference between setae and chaetae is that setae are bristle-like structures present in both vertebrates and invertebrates, while chaetae are chitinous bristle-like structures present in most fungal species.
Setae and chaetae are both bristle-like structures that mainly help in facilitating locomotion and attachment of the organisms. It is an important feature in living organisms for its survival. Therefore, through evolution, depending on the type of environment, the organisms are associated with different types of structures. Thus, setae and chaetae are structures that helped in the survival of organisms during evolution.
What are Setae?
Setae are bristle, hair-like appendages found in both vertebrates and invertebrates. Its singular term is seta. In invertebrates, it is mainly present in annelids and crustaceans. In annelids, the setae are stiff in nature. They help the annelids to attach to the surface and prevent backsliding during their movement. Furthermore, in some organisms, the setae act as the podia and enable movement. In crustaceans, setae mainly line the oral cavity and sometimes are differentiated into scales, which enable them the capture the pray. In some insects, setae are poisoned or have the ability to act as a defence mechanism.
The setae arise from the trichogen. It is also known as the bristle generator. They arise as hollow structures. Upon maturation, they undergo a hardening process and project through the secondary accessory cells. Then they generate a flexible membrane and develop into setae, macrotrichia, chaetae or scales.
Some vertebrates also have setae or similar structures. Some fungal and plant species also have similar structures; however, most are microscopic in nature.
What are Chaetae?
Chaetae are a specific type of setae that contain chitin in their hair-like bristles. Thus, these are also called as chitinous bristles or chitinous setae. They are mostly found in fungi; however, certain annelids also contain chaetae. Their main function is similar to that of setae. They are also involved in the attachment of the organism to the surface, facilitation of movement and sometimes help as defence modes.
In fungi, the chaetae are mostly microscopic. However, in some species, they can be observed under the hand lens. Similar to setae, chaetae also arise from the trichogen. Upon maturation, chitin deposits on the bristles to harden the structures.
What are the Similarities Between Setae and Chaetae?
- These are bristle-like structures or hair-like structures.
- Moreover, both arise from the trichogen and mature into harden structures.
- They form hollow tubes that later develop into hard bristles.
- Also, both are important in attachment, movement and as defence mechanisms.
- Both can be found in annelids.
- They are mostly microscopic in nature; however, in some organisms, it can be observed using a hand lens.
What is the Difference Between Setae and Chaetae?
Both setae and chaetae are very similar in structure and function to each other. However, the key difference between setae and chaetae is in the composition of the two structures. While setae consist of polysaccharides and lipids as their hardening material, chaetae comprise mainly of chitin.
The below infographic summarizes the difference between setae and chaetae.
Summary – Setae vs Chaetae
Setae and chaetae are two structures present in most annelids and crustaceans. The primary function of both is to act as bristle-like structures that facilitate attachment and locomotion. However, the key difference between setae and chaetae is that chaetae have chitin in the hair-like bristles, as opposed to setae. Chitin deposition takes place during the hardening process of the chaetae. Both have similar structures and arise from the trichogen and then mature into thick hair-like bristles. So, this is the summary of the difference between setae and chaetae.
1. Tilic, Ekin, and Thomas Bartolomaeus. “Structure, Function and Cell Dynamics during Chaetogenesis of Abdominal Uncini in SabellariaAlveolata (Sabellariidae, Annelida).” Zoological Letters, BioMed Central, 8 Jan. 2016, Available here.
1. “Isonychia Foreleg” By Erin Hayes-Pontius – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Syllid polychaete undergoing epitoky” By Megan McCuller – Own work (CC BY-SA 4.0) via Commons Wikimedia