Wrong! This is about a creature that is about as far away from a shark as you can get, I think. I'm talking worms. Hammerhead worms, to be exact. This thing...
When I pointed it out to Steve as it wriggled across our veranda, he said, "Cool! Looks to be some sort of planarian. Probably called a hammerhead or something similar." He's so smart. He hit the nail right on the head, so to speak.
These things are harmless...to people and most other creatures, at any rate. But if you are an earthworm or a snail or even other hammerhead worms (yes, they can be cannibalistic)...beware! Bipalia can track their prey.
And when they catch it, it's not pretty. The hammerhead worm uses its muscles and body secretions to attach itself to its prey. It then extends its mouth, found on the middle section of its body and secretes digestive enzymes onto the worm's body. Finally, it sucks up the liquefied worm juice.
Oh, by the way...don't think that just because you live in North America you are safe from these slimy creatures. Since 1901 they have been found in American greenhouses. There are at least four species of bipalia that are on the U.S. invasive species list, and they have become a real problem in the southern United States, especially for earthworm raisers, as there appear to be no predators that feed on their noxious bodies. They are also found in California, New York, Illinois, most northern states, coastal South Carolina, the Gulf states, and Pennsylvania.