SPONGE
Sponges belong to the phylum porifera. They do not have a digestive tract or respiratory system. They filter feed to get their nutrients from their environments. They are very inactive looking creatures which live on the sea floor and along coral reefs.
jellyfish
Jellyfish come from the Cnidaria, and vary immensely from the phylum Porifera. Jellyfish have tentacles which can sting and grasp their prey. Cnidarians have a digestive tract, and go through two distinct stages of life, while Sponges lack these features.
squid
The jump from sponges and jellyfish to squids is a large one. Squids have complex cells, actions and structures. Squids are able to change their color through the use of chromatophores, pigmented cells which allow for color change (like a chameleon). They have many organs, such as a digestive system, a heart, an inc sack, and a beak.
earthworm
Earthworms are pretty much a big digestive tract. Their digestive tract runs from end to end starting in a mouth and ending with an anus. They have segmented skin, which they also breathe through.
perch
The perch is very complex. It has specialized organs, such as an esophogus, a liver, a pancreas, a stomach, an intestine and an anus. They have a full skeletal system, which allows it to not get crushed by the weight of the ocean. It has many fins, which allows it to maneuver efficiently in the ocean.
frog
Frogs are a cornerstone species, and they are much more complex than any other animal on this list. They have powerful muscles in their legs that allow them to escape and jump great distances. They are amphibians, which means that they begin their life in the water, and end it with the ability to freely travel in the water and on the ground. There are many amphibians, such as newts and salamanders.