Once the food is trapped, the collar cells digest it (see Figure below). They also have a flagellum that whips the water and keeps it moving. Collar cells have tiny hairs that trap the particles. As the water flows by, specialized collar cells (which are also known as choanocytes) filter out food particles such as bacteria. The water flows through a large central cavity called the spongocoel (see Figure above). They pump water into their body through their pores. A sponge lacks tissues and organs, but it has several types of specialized cells. They grow from specialized cells in the body of the sponge. Spicules are made of silica, calcium carbonate, or spongin, a tough protein. A sponge endoskeleton consists of short, sharp rods called spicules (see Figure below). An internal skeleton is called an endoskeleton. Sponges have an internal skeleton that gives them support and protection. Root-like projections anchor them to solid surfaces such as rocks and reefs.

This means they are unable to move from place to place. Many species live in colonies that may be quite large. They range in diameter from about a centimeter (0.4 inches) to over a meter (3.3 feet). For example, they may be shaped like tubes, fans, cones, or just blobs. Sponges come in a variety of shapes and sizes. Can you predict the function of the pores?

This orange sponge is covered with pores. Almost all of them inhabit the ocean, living mainly on coral reefs or the ocean floor. There are at least 5,000 living species of sponges. As you can see from Figure below, a sponge has a porous body. Sponges are aquatic invertebrates that make up the phylum Porifera. Without the traits that evolved in sponges and other simple invertebrates, you would not exist. They also evolved some of the most important traits that are found in almost all animals today. Their continued existence is evidence that they are well adapted for their habitats.

Some, like the sponges you will read about in this concept, have existed virtually unchanged for hundreds of millions of years. However, simpler invertebrates evolved before insects. They are the most numerous animals on Earth. Invertebrates are animals without a backbone.

How do sponges move