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The fleshy protrusions on the sides of some marine gastropods are also called parapodia. They are particularly well-developed in sea butterflies. Some sea hares use their parapodia to swim. Parapodia can even be used for respiration (similar to gills) or for locomotion. Parapodia are found in the following taxonomic groups of gastropods:
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.
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.
Chaetae on the notopodium are called notochaetae and those on the neuropodium are called neurochaetae. Thick, internal chaetae that provide support for well-developed notopodia or parapodia are called acicula. A wide range of chaetal shapes and arrangements exists: [6] [1] [4] [5] Basic forms are capillaries and spines. Capillaries are the most ...
Setae in oligochaetes (a group including earthworms) are largely composed of chitin. [1] They are classified according to the limb to which they are attached; for instance, notosetae are attached to notopodia; neurosetae to neuropodia. [2] Diptera setae are bristles present throughout the body and function as mechanoreceptors.
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.
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.
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 ...