Differentiate between urochordates and cephalochordates,discuss their characteristics features with reference to protochordates.
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Answer:
urochordates:(1) adults are sedentary or fixed to substratum . (2) notochord is only present in tail of the larva and disappears in adult . (3)pharynx is perforated by numerous apertures called stigmata formed by larval gill slits (4) the larva is motile and undergoes retrogressive metamorphosis , change from better developed larva to less developed adult.
Cephalochordata: (1)both adult and larva are motile .(2)notochord extends throughout the body and is present in larva and adult throughout the life .(3)pharangeal gill slits are more numerous and are better developed .(4) It shows progressive metamorphosis ., change from less developed larva to well developed larva .
subphylum urochordata and cephalochordata are referred to as protochordates or acrania , whereas phylum hemichordata is also reffered to as protochordate .
so I will discuss their charaacteristic features with refrence to hemichordates or protochordates .
chordates ( cephalochordata and urochordata ) : (1)notochord is present , (2)central nervous system is hollow and dorsal (3)gill slits are present (4)tail is present (5)heart is present(6) if present RBC contain haemoglobin whereas in protochordates (1)notochord is not present (2)CNS is ventral and solid (3)gill slits are absent (4) tail is absent (5)RBC are absent(6) if any pigment is present it is in blood plasma .
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