Haemal System of Asterias or Sea star

 

Haemal System of Sea star 

In Asterias or sea star, the blood lacunar system as such is absent and its function has been taken up by a special system called haemal system, which consists of channels enclosed by coelomic spaces.

 

Axial Complex of Asterias:

A very well-formed axial complex com­prising of a coelomic cavity enclosing the stone canal and axial gland is present in Asterias.

The axial complex remains intimately associated with the inter-brachial septum. The axial sinus is a thin-walled tubular cavity which opens orally into the inner smaller ring of the hypo-neural ring sinus.

 

  

 

It opens aborally into the genital sinus and finally into the ampulla of the stone canal.

The axial gland is a long spongy body of brown or purple colour and gives a small terminal process at the aboral end. This process is surrounded by a contractile closed sac named as terminal sac or dorsal sac or madreporic vesicle. This vesicle is situated very close to the ampulla of the stone canal, but has no connection with it.

The axial gland terminates orally in the septum of the hypo-neural ring sinus. The axial gland is variously called as heart, ovoid gland, brown gland, septal organ and dorsal organ. The function of the axial gland and its relation to other systems is still disputed.

It has an interior core of connective tissue traversed by many spaces containing coelomocytes and externally it is covered by a coelomic epithe­lium.