I got more entries than I had anticipated, but, actually, the first guess I had came only minutes after I had posted the initial photos and contest info.
So, congratulations to Jen S. from Oakland, CA!
If you were curious, here is the answer and the reasons I detailed for my decision:
To be honest, it doesn't really look like a tapeworm, and there are a few reasons for this:
- Tapeworms are usually classified by the different shapes their "head" (more appropriately, scolex) because they use various hooks and suckers to attach to the gut wall. If you look at your worm's ends, there isn't a distinct sucker or any sort of texture that would indicate hooks.
- Tapeworms segments are all little sacks of eggs and/or reproductive organs, depending on the species. They mature as they move away from the scolex, further down the worm. They get larger and more defined as they move down, too. This worm seems to have regularly sized segments all the way down.
- The middle section that is a different color, see that? That resembles what most annelid groundworms have, called a "clitellum". Its usually much lighter in color, but that's the only thing I can think to compare it to.
- If this were a parasitic worm, it would not be a tapeworm, because they are generally flat, especially towards the ends that can break off. Most parasitic nematodes that take on the roundworm shape are not segmented, and most of them are too small to take up a large segment of a plate.
I think its safe to say that it is an Eisenia fetida, or a "Red Wriggler". They are used in composting (do you or your neighbors compost?), and can live in environments that are unnatural for most worms. They are found all over the UK. I think you, and your cats' backsides, will be totally fine.
- Since you did put it in water, and it wriggled around, it was probably doing its best to get towards some air. Have you noticed that groundworms and snails like to come out during the rain? That's usually because the ground absorbs too much water. Their tunnels and burrows in the ground fill up, and they don't have access to the appropriate balance of oxygen and moist environments.
Problem solved. Thanks, scientific reasoning!
Also, big thanks to everyone who entered their guesses.