The 1958 horror film The Blob was inspired by a real event in 1950: a close encounter between four police officers and a star jelly.
Back in 1950s Philadelphia, four police officers apparently encountered a gelatinous blob disc near the Philadelphia Gas Works. It was two metres wide, 30 centimetres high, and when they picked it up the whole thing dissolved. This event inspired the 1958 horror film The Blob. In that film, the blob falls to Earth inside a meteorite. It absorbs a few victims, grows larger at an alarming rate, and threatens a small Pennsylvanian town. But the 1950 blob was not the first such encounter: records of so-called “star jellies” date back at least seven hundred years.
Late Medieval and Early Modern sources describe the star jelly as a kind of blobby mass hatched from falling stars which disintegrates with a touch, as in this poem from 1676:
Like to a Star-faln Gelly in the night,
War with the Devil
A false appearance and deceiving vapour,
An Ignis Fatuus, and a short-liv’d Taper,
A madness and a folly void of reason,
Or like dead Salt, when it hath lost its season.
The “star-faln Gelly” comes up three years later in John Dryden’s scathing review of the Chapman play Bussy D’Ambois:
but when I had taken up what I supposed a fallen star, I found I had been cozened with a jelly; nothing but a cold dull mass, which glittered no longer than it was shooting.
The Cambridge History of English and American Literature
As much as I love the idea of interstellar goo meteorites, the connection to falling stars is probably fictitious. Instead, we have a few Earth-bound candidates for the star jelly.
First, slime moulds like the one pictured at the top of this post, or the translucent fungus also known as crystal brain:
Another candidate is a type of algae called Nostoc. Nostoc colonies are usually more or less invisible, but swell up in rain and form large jelly blobs:
And, finally, there’s the possibility that star jelly sightings are actually regurgitated toad and frog oviducts. Apparently birds eat the poor amphibia but are unable to digest some of the reproductive tract, so they barf the quivering gelatinous mass up. I do not have a photo of this one, thank goodness.
[Thanks to Siobhan L.]
The Generalist Academy 
When I was in high school, we had a pet slime mold in our biology class. Yes, my teacher was weird, and I loved her for it.