- Perihaemal system.
- Haemal system.
- Axial sinus: It is a small tube. It encloses stone canal and axial gland forming an axial complex.
- Aboral ring sinus: It is five sided sinus found inside the aboral wall of the central disc. It is incomplete in the region of the canal.
- Genital sinuses: Each gonad is encircled by a small genital sinus. It is connected with the aboral ring sinus by very small branch.
- Oral ring sinus: It is present around the mouth. It is divided into two
a) A smaller inner ring. b) A larger outer ring. The oral end of the axial sinus communicates with the inner division of the ring sinus.
- Radial perihaemal sinuses: It arises from the outer division of the oral ring sinus and goes into each arm. This sinus in each arm is divided into two by septum. Small, thin branches are given from the radial perihaemal sinuses into the podia.
- Marginal sinuses: Longitudinal marginal sinus is present just aboral to the marginal nerve cord.
- Peri-branchial sinuses: These are present in the form of circular spaces encircling the basal parts of the gills.
The mouth is surrounded by a oral haemal ring. This runs into the septum dividing the hyponeural ring sinus. From the oral haemal sinus arises radial haemal sinuses. Each one enters into one arm.