Porifera
The simplest phylum, there's not much to a Porifera animal. Porifera means "pore-bearer". The one main animal in the Porifera phylum is a sponge. Sponges are so simple that they used to be thought of as a plant because they don't move place to place like most animals. They don't have heads, arms, or legs, and they don't have any internal organs. Sponges mainly live in salt water, but there are a few kinds that live in fresh water. Sponges are asymmetrical, which means that they don't have symmetry. The sponge is hollow on the inside and also has a large opening at the top, called an osculum. All adult sponges are sessile. Sponges eat other living creatures to get the nourishment that they need to live. To obtain their food, they filter the food from the water as it gets sucked in through its pores (holes) called Ostia on the sides of their bodies. Algae, bacteria, and protozoa are filtered from the water as the water flows through the sponge to be used as food. Organisms that get food this way are called filter-feeders.
Sponges are made up of two layers of cells. The outer cells are called covering cells, and they are thin and flat. The inner layer of cells has flagella, which are little whips, and are called collar cells. The little flagella on the collar cells pump the water through the sponge's pores and then pump the water through the top of the sponge. The sponge's food is trapped and digested by the collar cells. The collar cells also help to bring in oxygen from the water. The jellylike middle layer has a special cell called a wandering cell, which carries food and oxygen to all the parts of the sponge and also collects waste to given off into the passing water. The middle layer also contains small, needle-like support structures called spicules, which link together to form a simple skeleton that supports and shapes the body of the sponge. A cool thing about the sponge is that it can reproduce sexually or asexually. When the sponge reproduces asexually, it forms another little sponge on its body called a bud on the parent sponge. This is called budding. The bud then breaks off from the parent when it is fully developed and swims off to find a place to live. The other asexual way is for the sponges to regenerate. If the sponge is cut up into pieces, each piece starts to grow back its missing body parts. -hr
Sponges are made up of two layers of cells. The outer cells are called covering cells, and they are thin and flat. The inner layer of cells has flagella, which are little whips, and are called collar cells. The little flagella on the collar cells pump the water through the sponge's pores and then pump the water through the top of the sponge. The sponge's food is trapped and digested by the collar cells. The collar cells also help to bring in oxygen from the water. The jellylike middle layer has a special cell called a wandering cell, which carries food and oxygen to all the parts of the sponge and also collects waste to given off into the passing water. The middle layer also contains small, needle-like support structures called spicules, which link together to form a simple skeleton that supports and shapes the body of the sponge. A cool thing about the sponge is that it can reproduce sexually or asexually. When the sponge reproduces asexually, it forms another little sponge on its body called a bud on the parent sponge. This is called budding. The bud then breaks off from the parent when it is fully developed and swims off to find a place to live. The other asexual way is for the sponges to regenerate. If the sponge is cut up into pieces, each piece starts to grow back its missing body parts. -hr