TRUNK-It comprises the entire body only the head and the last body segment the pygidium.It consists of 80-200 similar segments the pygidium.each broader than long and characterized by the presence of a parapodium on each lateral side.
PARAPODIA-The parapodia are antero-posteriorly flattened vertical flap like outgrowth of the body wall on the lateral sides of the trunk segments.The parapopodia are hollow structures enclosing coelom which is continuous with that of the trunk segments.The parapodium is typically biramous it consists of a proximal basal region bearing distally two parts a dorsal notopodium and a ventral neuropodium The parapodium part is further subdivided into two leaf like lobes or lingulae a dorsal superior lingula and a ventral inferior lingula.The each part of parapodia bears a base slender ,tentacular process known as cirrus ,the dorsal cirrus borne dorsally by the notopodium is slightly larger than the ventral cirrus.The each part of parapodia is supported internally by a deeply -embedded long stout and black chitinous rod known as aciculum.The aciculum also serves for the attachment of setal muscles thus serving as a sort of endoskeleton.Each part bears a bundle of long fine stiff chitinous bristles the setae or chaetae which project beyond the setae or chaetae which project beyond its margin. Each seta is lodged in a setal or setigerous sac,formed by the inpushing of the epidermis and base of the sac.The setae can be protruded ,retracted or turned in various directions with the heip of the setal muscles. Each seta is a two-jointed structures with a proximal shaft and a distal blade.The long bladed has a small shaft and a long slender straight and pointed blade with one edge serrated.The typical has a large stout shaft and a short ,stout blade with an incurved notched tip.The oar-shaped of seta occurs in the sexual phase or the heteroneresis in which the blade becomes oar-like.The sharp setae are used for protection and for obtaining a hold on the smooth inner walls of the burrows.
PARAPODIA-The parapodia are antero-posteriorly flattened vertical flap like outgrowth of the body wall on the lateral sides of the trunk segments.The parapopodia are hollow structures enclosing coelom which is continuous with that of the trunk segments.The parapodium is typically biramous it consists of a proximal basal region bearing distally two parts a dorsal notopodium and a ventral neuropodium The parapodium part is further subdivided into two leaf like lobes or lingulae a dorsal superior lingula and a ventral inferior lingula.The each part of parapodia bears a base slender ,tentacular process known as cirrus ,the dorsal cirrus borne dorsally by the notopodium is slightly larger than the ventral cirrus.The each part of parapodia is supported internally by a deeply -embedded long stout and black chitinous rod known as aciculum.The aciculum also serves for the attachment of setal muscles thus serving as a sort of endoskeleton.Each part bears a bundle of long fine stiff chitinous bristles the setae or chaetae which project beyond the setae or chaetae which project beyond its margin. Each seta is lodged in a setal or setigerous sac,formed by the inpushing of the epidermis and base of the sac.The setae can be protruded ,retracted or turned in various directions with the heip of the setal muscles. Each seta is a two-jointed structures with a proximal shaft and a distal blade.The long bladed has a small shaft and a long slender straight and pointed blade with one edge serrated.The typical has a large stout shaft and a short ,stout blade with an incurved notched tip.The oar-shaped of seta occurs in the sexual phase or the heteroneresis in which the blade becomes oar-like.The sharp setae are used for protection and for obtaining a hold on the smooth inner walls of the burrows.
No comments:
Post a Comment