Question

What are chitinous setae? Where are they present?

Answer 1

Hint:Setae are bristle or hair-like structures present on living organisms. Arthropods have a semi-transparent, tough exoskeleton which is chitinous.

Complete answer:
Chitinous setae can be found in Annelids and arthropods. Annelids have stiff setae which are bristles like projections present on the body. They help organisms to attach to the surface, thereby preventing backsliding during peristaltic movement. It is due to these structures that pulling a worm straight from the ground becomes difficult. Setae in oligochaetes are largely composed of chitin and are therefore called chitinous setae. They can be classified based on the limb they are attached to; for example, setae attached to notopodia are called notosetae, neuro setae are the ones attached to neuropodia.
Crustaceans have setae which are of two types, mechanosetae and chemosensory setae. In crustaceans, the setae are present especially on the mouthparts and may also be present on grooming limbs. Sometimes, setae are modified into scale-like structures. The function of setae present on the legs of krill and other small crustaceans is to help them to collect phytoplanktons, it helps in capturing them and allows them to get eaten.
Setae are present on the integument of insects, i.e. arthropods. These setae are unicellular, each one of the setae is formed by a single epidermal cell called trichogen, which literally translates to bristle generator. The setae in arthropods are hollow initially and remain hollow in most forms even after hardening. They grow and are projected through a tormogen, a secondary cell type, whose function is to generate the flexible membrane which connects the base of setae to the integument.

Note: Setae can be called hairs, macrotrichia, chaetae, or scales depending on their form and function. The membrane of setae is not cuticularized and therefore, movement is possible. Some insects use setae as a defense mechanism, setae of such organisms cause dermatitis when come in contact with the skin.