Simple animals? Okay, first, there are no simple animals. They are extreme in their own way, you just cant see them. Like dogs, they have better hearing then us humans and can see in the dark. And Bees, they dont see the world like us they see it in ultra-violt.
And cats. They can squeez into a hole the size of your palm.
So dont ask what is the simpliest animal, because we humans are kind of below the talents animals have.
The simplest animals don't have any circulatory or nervous systems. These are jellyfish and Myxozoa. Myxozoa are a group of parasites, that, in many cases are single celled.
They are, indeed, the most simplest multi-cellular marine animal
the simplest animal is a flat lichen called a trichoplax, has no sensory organs is just a microscopic bunch of cells.
ameoba
ProtozoaProtozoaProtozoaProtozoa
which of these is most primitive vertebrate??? (a)hag fish (b)lampray (c)placoderms (d)shark
Cnidarians
The sponge.
any animal with a spine or similar. the simplest being known as a notochord. it can also be said that any animal descendant from Haikouichthys is a vertebrate.
ribbon worm
Amoeba sponges
One of the most simplest cells are the animal cells.It only contains a nucleus, a cytoplasm and a cell membrane.
Organism.