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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 .
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 ...
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]
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 ...
Some tentacular cirri are present. The anterior parapodium points forward and has tapered ventral cirri. The posterior parapodium has cushion-like cirri. The setae include winged capillaries and pseudocompound forms on the anterior parapodia and winged capillaries, comb-setae and acicular setae on the posterior ones. [2]
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.
The parapodia on segments 13, 14 and 15 are fused into three paddle-shaped, piston-like structures, the purpose of which is to pump water through the tube. The water is drawn in through the anterior end and expelled through the posterior end, [ 1 ] passing through the fine mesh of the mucus bag where food particles get trapped.