Sponges

= __**Porifera**__ = media type="youtube" key="1ZcAzQLrEVI" height="385" width="480" Sponges http://wintersscience.wikispaces.com/Porifera%20video

on the top where water leaves
 * Sponges are aquatic (mostly marine)
 * Sessile
 * have two layers of cells
 * have pores on sides where water enters and an osculum
 * 10,000 known species



In the past, people thought sponges were plants because they did not move from place to place like most animals. All sponges are invertebrates that live in water. They are mostly marine but a few live in freshwater. These invertebrates are the simplest of all the animals. They do not have heads, arms, legs, or any internal organs. Sponges attach themselves to plants or rocks on the ocean floor. The adult sponge is **__sessile__**. Porifera are asymmetrical, meaning that they cannot be cut in two to form some sort of symmetry.

Scientists observed the sponge and discovered that it obtains its food the same way other animals do. It eats other living organisms to get nourishment. A sponge **__filters__** its food from the water as it pulls the water through the pores or holes (ostia) on the sides of its body. Bacteria, algae, and protozoa are filtered out of the water as it flows through the sponge to be used as food. Porifera are filter-feeders. A sponge body is made up of two layers of cells. The outer layer of cells are thin, flat cells called **__covering cells__**. The inner layer of cells has **__flagella__** and are called **__collar cells__**. The flagella on the collar cells pump the water through the pores and then out through the top of the sponge. The food is trapped and digested by the collar cells. Collar cells also help bring in oxygen from the water. The jellylike layer between contains a special cell called a **__wandering cell__**. The wandering cell carries food and oxygen to all of the parts of the sponge and collects wasted to be given off into the water passing through the sponge. The jellylike middle also contains small needle-like support structures called **__spicules__**. The spicules link together to form a simple skeleton that supports and shapes the body of the sponge. The body of the sponge is sort of like an empty sac. The sponge is hollow on the inside and has a large opening at the top where all of the water leaves the sponge called the **__osculum__**.

Sponges reproduces both sexually and asexually. Sexual reproduction occurs when eggs and sperm are released into the the water where they hopefully meet up to produce new sponges with DNA from two different parents. Asexual reproduction occurs with the sponge **__budding__**. A bud grows off of the side of a large sponge and eventually drops off and lands somewhere else in the water where it grows into a mature sponge. Sponges can also **__regenerate__** if they are broken into pieces. This means that the pieces can each grow into its own sponge. Therefore, if a sponge is broken into three pieces you will get three new sponges.