Plastic Jellyfish Aquarium

What is this white gelatinous mass that appeared in my plastic glass?

I use a plastic glass as an aquarium, for growing some algae. I have inside my plastic glass:
“Pleurococcus vulgaris” algae
Water
Nutrients

Suddenly, a transparent gelatinous mass that looks like a jellyfish appeared out of nowhere inside my plastic glass. How can explain it?

You may have some bacteria colonizing your plastic glass. Once the algae colonies started growing, some of them naturally died. Their remains are now food for other organisms. You’re actually developing a little ecosystem in your glass.

Jellyfish LED Aquarium

[affmage source="ebay" results="30"]Plastic Jellyfish Aquarium[/affmage]
[affmage source="amazon" results="10"]Plastic Jellyfish Aquarium[/affmage]