Sponges are one of the animals that filters water for it food. A sponge has two cell and between the two cells is a jelly like substance that has cell that can carry the food throughout its body. On the outer cell there are holes that are called prose. There are also 5000 different kinds of sponges.
A mollusk is has a soft body with no bones. The name comes from the Latin word mollus meaning soft. The shell of a mollusks is formed by an organ called the mantle. Mollusks also mold or shied
A flat worm has a body, a digestive system. Flat worms can live in fresh water like streams lakes and ponds. They are usually small most are less than 30 mm. During daylight they can be found under rocks or in the mud at the bottom. They also lay eggs.
A round worm has long tube like body. Most round worms are to small to be seen with the naked eye. A round worm has a digestive system with two openings. A round worm has a nervous system with a brain and other simple sense organs.
Many parasitic worms have a life cycle that needs two species of host animals some of these parasitic live in fresh water snails. Parasitic can cause lots of disease over 2 million people in tropical parts of the world die because of these parasitic.