Parazoa facts for kids

Parazoa are a special group of animals. They are often called a "sub-kingdom" because they are very simple compared to most other animals. The most famous Parazoa are sponges, which belong to the group called Porifera. There are about 15,000 different kinds of sponges all over the world!

Even though sponges are made of many cells, they don't have true tissues or organs like humans or other complex animals. Their cells can even move around inside them to do different jobs. Another type of Parazoa is called Placozoa, which includes tiny, flat, see-through animals like Trichoplax adhaerens. They are even simpler than sponges, with only a few cell types.

Sponges: Simple Animals of the Water

Sponges are amazing animals that live in water. They are known for their bodies being full of tiny holes, or pores. These pores are super important! They let the sponge filter food and nutrients from the water that flows through them.

You can find sponges in many places, from shallow ocean waters to deep freshwater lakes. They come in all sorts of colors, sizes, and shapes. Some sponges can grow as tall as a person, while others are tiny, smaller than a grain of sand! Their shapes, like tubes, barrels, or fans, help water flow through them perfectly.

How Sponges Live and Eat

Sponges don't have many of the body systems that other animals do. They don't have a heart, lungs, stomach, muscles, or a brain! Instead, the water flowing through their pores helps them breathe and get food.

Sponges usually eat tiny things floating in the water, like bacteria and algae. Some bigger sponges might even catch small crustaceans, like krill or shrimp. Since sponges can't move around, they usually stick to rocks or other hard surfaces in the water.

Sponge Body Structure: Pores and Layers

Most sponges don't have a symmetrical body shape, meaning they aren't the same on both sides. This is different from most animals, which usually have radial (like a starfish) or bilateral (like a human) symmetry. Sponges are considered the simplest animals and are related to very early life forms.

The body of a sponge is covered in many small holes called ostia. These holes lead to canals that bring water into the sponge's inner chambers. One end of the sponge is attached to a surface, while the other end, called the osculum, is open to the water.

A sponge's body wall has three main layers:

• Pinacoderm: This is the outer layer, like the skin of a sponge. It's made of flat cells called pinacocytes. These cells can shrink, making the sponge smaller if it needs to.
• Mesohyl: This is the middle layer, a jelly-like substance. It contains special cells called archaeocytes. These cells can move around and change into other types of sponge cells. They help with digestion, moving nutrients, and even making sex cells. Other cells here, called sclerocytes, make tiny hard bits called spicules that give the sponge its support.
• Choanoderm: This is the inner layer, made of cells called choanocytes. Each choanocyte has a whip-like tail called a flagellum. When these flagella wave, they create a current that pulls water through the sponge's body.

Sponge Body Plans: Different Ways to Filter Water

Sponges have different ways their pores and canals are arranged. There are three main types of body plans:

• Asconoid: These are the simplest sponges, shaped like a tube with an open internal space (spongocoel) lined with choanocytes.
• Syconoid: These sponges are larger and a bit more complex. They have a thicker body wall and canals that are more developed.
• Leuconoid: These are the most complex and largest sponges. They have a very detailed system of canals with many chambers. Each chamber is lined with choanocytes that direct water flow through the sponge and out the osculum.

Sponge Reproduction and Life Cycle

Sponges can make new sponges in two ways: sexually and asexually. Sexual reproduction is the most common way. Most sponges are hermaphrodites, meaning one sponge can produce both male cells (sperm) and female cells (eggs).

Usually, a sponge will release only one type of cell at a time. Sperm cells are released into the water and carried by currents to another sponge. Inside the receiving sponge, choanocytes capture the sperm and guide it to the mesohyl layer, where the egg cells are.

Once a sperm fertilizes an egg, a tiny larva develops. This larva then leaves the sponge and swims around until it finds a good place to attach itself. Once attached, it grows and develops into a new adult sponge.

Images for kids

• Barrel Sponge - Parazoa.jpg

  A barrel sponge, a type of Parazoa.

See also

In Spanish: Parazoa para niños