In our hydrae experiments, yes, they came with the lake water .. you can see some pictures here if you're interested, there's a video of the battle between nematode and hydra as well - I did this experiment with my kids many times over the years, its always fascinating to see what grows and what eats and what stays behind ..

https://imgur.com/user/waterplusalgaeequalshydra

Bonus retro-computing stuff there too.. ;)

>Triops eggs

Let me know how it goes! I love the Triops arena ..