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takyon [soylentnews.org] writes:

Most animals have a circulatory system that pump bloods. Sea spiders have a digestive system that can move both food and blood [sciencemag.org]:

Researchers discovered the remarkable physiological strategy after injecting dye into sea spiders—common inhabitants of the world's oceans named for their resemblance to land-based spiders—and watching the flow of blood. They noticed that the animals' hearts were beating weakly. But the digestive system—which is unusually extensive in sea spiders, running down each leg—was contracting in waves, moving food in the gut as well as blood in the surrounding hemocoel cavity, the spider equivalent of veins and arteries.

Respiratory gut peristalsis by sea spiders [cell.com] (DOI: 10.1016/j.cub.2017.05.062) (DX [doi.org])

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