It was both modern and unsophisticated. A simple, tubelike heart was buried in the creature’s belly—or thorax—and shot single blood vessels into the 20 or so segments of its primitive body. In contrast, x-ray scans of the specimen revealed profoundly intricate channels in the head and neck. The brain was well supplied with looping blood vessels, which extended branches into the arthropod’s alienlike eyestalks and antennae and rivaled the complexity of today’s crustaceans.
The study of cardiovasculature is actually extremely important to understanding neuroscience. There is a complicated apparatus in the brain designed to interact with the vasculature in order to get ATP (energy), etc. Though a commenter (Ginny Freeman) notes:
The “heart” was NOT buried in the “creature’s belly”. It’s a crustacean, for heaven’s sake! Crustaceans like all arthropods have a DORSAL circulatory system.
Here is the original paper.