Heart and blood-vessels are entirely absent; the blood is contained in sinuses which have no distinct walls or endothelial lining, and the principal of which are the perianal, the pedal, the visceral and the pallial.
It is remarkable that in Scaphopoda only among Mollusca the blood-spaces are in communication with the external medium: a pair of apertures near the renal openings lead from the perianal sinus to the exterior and allow the blood to escape during violent contractions of the body.
The perianal sinus.
The larva is provided with postoral and perianal ciliated bands, and on either side with a bunch of long provisional setae.
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