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Balanoglossus will show open type of blood vascularsystem. It shows
 
  1. Blood
  2. Dorsal sinus
  3. Heart
  4. Afferent vessel
  5. Distributing vessels
  6. Collecting vessels.
 
1. Blood: It is in liquid form. It is colourless. It has no haemoglobin. It contains few blood cells.
 
2. Dorsal sinus: In the proboscis above the buccal diverticulum a dorsal sinus is present. In this biood flows from posterior end to anterior end. It gets blood from collecting blood vessels. At the antei ior end it will push the blood into afferent blood vessel.
 
3. Heart: It present above the dorsal sinus. It is triangular in shape. It shows contractions and relaxation. This brings movement in dorsal sinus.
 
4. Afferent blood vessel: From anterior end of Dorsal sinus afferent blood vessels will arise. They unite to form a plexues. This is called glomerulus. This works as a excretory organ.
 
5. Distributing vessels: From glomerulus blood will enter into 4 blood vessels.
 
  1. Mid dorsal proboscis artery hill supply blood to proboscis parts.
  2. Mid Ventral Proboscis artery supplies blood to ventral side
  3. Two afferent glomerular arteries wilffravel backwards and unite to form ventral artery.
  4. Ventral artery: It is muscular. It travels to the end of trunk. Blood flows backwards in this blood vessel. This gives the following blood vessels. 
    a) Ventral collar blood vessel 
    b) Ring blood vessel in collar 
    c) Afferent branchial vessel carry blood to gills of pharynx.
 
6. Collecting blood vessels: It travels on the dorsal side. It is muscular.

It will collect blood from all body parts. This vessel will supply blood to the dorsal sinus.
 
Thus blood flows in the blood vascular system.

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