cnidaria
I think Porifera - sponges. You can take them apart cell by cell and they will still regenerate. But it´s not certain they can be grouped with the animals at all, so Cnidaria (jellyfish and anemones) could be correct too. Just keep in mind Porifera comes before Cnidaria.
Sponges from the phylum Porifera. The simplest of all animals. They are the only animals that do not have a nervous system of any kind.
sponges
Probably the simplest animal forms would include or Porifera. These animals have no central nervous system and very little symmetry.
The sponge is the simplest animal, but I'm not sure if that's the answer you're looking for.
A Sea Sponge
sponges
Protozoa
they are put into a group called invertebrate's
An invertebrate that has a soft body and a shell is called exosceloton.
Oysters belong the the invertebrate group of mollusk.
the most complex group of invertebrate is cnidarians
Insects are the largest and most common invertebrate group.
They are in the mollusks group.
the posaidon group
invertebrate
no
They belong to the group of arachnids.
A spiny skinned invertebrate is called a sand dollar. That is because they are are echinoderms (a type of invertebrate),
mollusk, polycepodaIntelligent Invertebrate: The octopus - a cephalopod - is one of the largest, fastest and most intelligent of all invertebrates.This information was taken from "Animalplanet.com".