Thursday, 26 January 2012

HEMICHORDATA-CHARACTERS

It include marine,solitary or colonial and mostly tubicolous.
Body is soft, fragile,vermiform,unsegmented,bilaterally symmetrical and triploblastic.
Body is divided into three regions proboscis,collar,and trunk.
Body wall of a single-layered epidermis with mucuous glands.
Coelom is enterocoelous, usually divided into protocoel,mesocoel and metacoel.
Digestive tube complete,straight or u-shaped.
Ciliary filter feeders.
Circulatory systems simple and open.
Excretion by a single proboscis gland.
Nervous system primitive.Dorsal collar nerve cord hollow.
Reproduction mainly sexual.
Fertilization external in sea water.Leads to tornaria larva.


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