Parapodium

-:Parapodium:-

All the segments excepting the first and the last segments bear on either lateral side a fleshy,flat and hollow parapodium. Largest parapodia are encountered in the middle segments of the body,then the size of the Parapodia decreases towards the two ends. Each parapodium is biramous in nature.
It consists of a basal part and two distal parts-
>Dorsally placed notopodium*.
>Ventrally placed neuropodium*.
Both these parts are sub-divided into lobes and both of them carry pack of needle-like structures, called setae which project beyond the lobes.


Cirrus (Pl.cirri):-
              The dorsal and ventral sides of the parapodium bear small, tentacle-like, cylindrical appendages, called dorsal and ventral cirrus respectively. The ventral cirrus situated ventral to the neuropodium,is smaller than the dorsal cirrus situated dorsally on the notopodium.
Setae:-
        The setae are stiff,niddle like chitinous rods which remain in bundle may be moved in other directions with the help of muscles. One of the setae in each bundle is long,rod-like and dark in colour. It is known as aciculum and it projects on the surface. Each seta consists of a basal shaft*with which articulates a terminal blade.
Three types of setae are seen-
>In one type of the shaft is oar-shaped
>In the second type shaft is slender and the blade is narrow, straight and elongated.
>In the other type the shaft is comparatively thicker and the blade is small and curved.


Functions:-
The Parapodia perform the following  functions-
>The Parapodia are modified variously in different polychaeta and perform different Locomotory functions,such as crawling*and swimming*. The Parapodia in some polychaetes are highly  highly vascularized* structure and function as respiratory organs.