What job(s) do these parts of a cnidarian have?
1.cnidocytes
2.gastric cavity
3.Ectoderm-outer cell layer of a cnidarian
4.nematocyst
5.inner cell layer of a cnidarian

When you are making a guess you are forming a hypothesis

Many archeologists and anthropologists disagree with dr. thorne's view.  thorne strongly believes that what many calls "homo erectus"  was in fact  homo sapiens,  and that they migrated out of africa almost 2 million years ago and dispersed throughout europe and asia. that's way different  from what scientists have always believed about the evolution of the species.

Although i don't know what is the simulated system, starfish are predators that eat mostly  microalgae,  snails, sponges, bivalves, mussels and other small marine animals. removing starfish from any system would definitely increase this animals that they prey.