Some of the most horrific images in high school biology textbooks depict parasitic tapeworms blocking the intestines of humans, or inside an unfortunate dog or cat. But not all flatworms are parasites, and their free-living cousins are capable of equally gruesome feats of nature. The slender flatworm Euplana gracilis consumes its victims by sucking out their insides, as displayed in the video above from benthic ecologist Dean Janiak.
It starts by wrapping its body around the dorsal (back) side of its prey–in this case, a shrimp-like amphipod. A massive struggle ensues until the amphipod is completely immobilized. Then the flatworm begins to feed. Sticking its tube-like pharynx through a segment of the amphipod, the flatworm consumes and digests its internals–a process that takes about half an hour. Once finished, it abandons the empty carcass and goes into a resting period until its next meal. On the outside, an amphipod that’s been eaten doesn’t look that different from a normal amphipod…except for the fact that it’s, well, dead.