An explanation of the anatomical features seen in this specimen has now been published.
Fuchs et al. 2015. A nearly complete respiratory, circulatory, and excretory system preserved in small Late Cretaceous octopods (Cephalopoda) from Lebanon. Paläontologische Zeitschrift

The branching structure at the back of the animal is interpreted as gonad capillaries.
The blood sinus is preserved in front of the ink sac.
The large triangular objects are the nephridial sacs, from which first and second order afferent branchial vessels extend forwards and branchial hearts with ramus stellaris and ramus superior extend laterally.
Lastly the posterior vena cava extend behind the nephridial sacs.