RYE, N.H.  The culprit sat in an open trash bag baking in the hot sun, raked to shore by a pitchfork-wielding lifeguard who paddled out on a surfboard.

Staring down in wonder  and disgust  at the huge jellyfish carcass at Wallis Sands State Park, Simon Mayer of Rye asked, “Is that the monster?”

It was to some, and it was doing plenty of posthumous damage. About 150 people were stung Wednesday by what officials said was a lion’s mane jellyfish weighing nearly 40 pounds, which turned the tranquil beach into a frenzied sea of screaming children and aching adults with red, sore feet and legs.

It was not the blob of dead jellyfish, but rather pieces of its stinging tentacles that stung the waders, scientists said. Jellyfish can still emit toxins when dead or broken apart, said Renee Zobel, a marine biologist with the New Hampshire Fish and Game Department.