Here's for all the sci-fi fans out there.

It looked like a worm at first glance.
Upon closer inspection, however, Jack realized that the creature had legs--tiny, feather like limbs that churned at the water like spinarettes to propel the little creature along. Its body was three inches long, and was divided into segments that seemed to fold and unfold like an accordion as it moved.
Jack though it was dark brown in color, but when he looked closer, he saw that it was, in fact, transparent. The chitin armor that covered it was clear, and through it, Jack could see its long, squishy brown stomach and the blackish, coiled spaghetti structure of its intestines. There were several pea-sized blogs that could have been its heart or kidneys, and a long, brown tube that extended towards the head end of its body.
Its head, Jack was only able to identify by process of elimination. It didn't appear to have any eyes, a nose, or a mouth, but that end wiggled a little more than the other, and Jack watched as it accordion-jumped after a beetle-like insect in the water. The beetle seemed panicked, though Jack couldn't see any reason for it to be, since the worm-thing didn't appear to have any way to eat it. Perhaps the beetle was simply afraid because the worm was bigger than it.
The worm was faster, too, and it managed to catch up with the beetle with one final jump that propelled it a full six inches through the water. The beetle made a panicked clicking noise as the worm closed in on it, and made one last futile attempt to twist out of the way.
It was then that Jack discovered that the worm did in fact have a mouth.
The tip of the worm's 'head' suddenly stretched open to the size of a penny, revealing hundreds of tiny, pinkish-gray needles that lined the creature's maw in a circle, layered in inward-facing rows that pointed down into its gullet. The beetle struggled as the teeth bit into its shell, but within seconds it was dead, and the worm had only to suck the remains of its prey down into its stomach, where Jack saw its innards turn from brown to black as its digestive juices began to work.
Jack fought back an urge to throw up, and instead used the heel of his boot to crush the see-through worm into a jellylike smear on the ground.
Unfortunately, that proved to be a near-fatal mistake.

I never finished this story, nor does it really have a beginning. I got the idea at a fly fishing convention, where one booth was displaying river creatures caught in the Apple River in tanks and water-filled trays. Amongst the numerous crayfish, boatmen beetles and dragonfly nymphs, there was also a bunch of worm-like invertebrates that I'm pretty sure were cranefly larvae. They were partially see-through, and it reminded me of some ghost shrimps I saw at Wal-Mart that I could actually see digesting their food. I expanded on it, and the result was this.
As to Jack's near-fatal mistake, I'll say only that the worm-thing was merely a larva.