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In invertebrates, the term parapodium (Gr. para, beyond or beside + podia, feet; pl.: parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids , where they are paired, unjointed lateral outgrowths that bear the chaetae .
In Polychaeta, chaetae are found as bundles on the parapodia, paired appendages on the side of the body. [1] The chaetae are epidermal, extracellular structures, and clearly visible in most polychaetes. They are probably the best-studied structures in these animals. [2] Segments bearing chaetae are called chaetigers. [3]
Parapodia are mostly biramous (only the first two pairs are uniramous). Peristomium fused with the first body segment, with usually two pairs of tentacular cirri. The first body segment with 1-2 pairs tentacular cirri without aciculae. Compound setae are present.
Setae on the foreleg of a mayfly. Annelid setae are stiff bristles present on the body. They help, for example, earthworms to attach to the surface and prevent backsliding during peristaltic motion. These hairs make it difficult to pull a worm straight from the ground. Setae in oligochaetes (a group including earthworms) are largely composed of ...
Polychaeta (/ ˌ p ɒ l ɪ ˈ k iː t ə /) is a paraphyletic [1] class of generally marine annelid worms, commonly called bristle worms or polychaetes (/ ˈ p ɒ l ɪ ˌ k iː t s /).Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin.
The main body consists of repeating segments called chaetigers, each with a pair of parapodia containing setae, the function of which varies depending on where on the body the chaetiger is located. The body of D. claparedii may have between 35 and 150 chaetigers, and those near the posterior and anterior ends have hook-like setae to assist with ...
Nereis possess setae and parapodia for locomotion and gas exchange. [1] They may have two types of setae, which are found on the parapodia. Acicular setae provide support. Locomotor setae are for crawling, and are the bristles that are visible on the exterior of the Polychaeta.
Hence annelids' chetae are structurally different from the setae ("bristles") of arthropods, which are made of the more rigid α-chitin, have a single internal cavity, and are mounted on flexible joints in shallow pits in the cuticle. [8] Nearly all polychaetes have parapodia that function as limbs, while other major annelid groups lack them.