Others have tiny, hard particles called spicules. Some sponges have a soft network of protein fibers called spongin. The body of the sponge would collapse if it did not have some type of supporting structure. Color all of the amebocytes (E) green – look for them carefully. Because of the amebocytes, scientists believe that sponges evolved from protists. The job of the amebocytes is to travel around distributing food and oxygen to the cells of the epidermis. In the jelly-like substance between the epidermis and the collar cells are cells called amebocytes – because they look like amebas. Color the inside of the sponge where water circulates the same light blue as you colored the incurrent pores. Color the osculum (D) dark blue, the incurrent pores (C) light blue. As water passes through the sponge in this way, cells absorb food and oxygen and waste is excreted. They do this by swishing their flagella which pulls water through the incurrent pore – water then travels out the osculum at the top of the sponge. The inner layer consists of collar cells (A) whose function is to circulate water through the sponge. Color all the epithelial cells (B) of the epidermis peach or pink. The outer layer of the sponge is the epidermis which is made of flat cells called epithelial cells. The primitive structure of a sponge consists of only two layers of cells separated by a non-living jelly like substance. Sponges exhibit less specialization (adaptation of a cell for a particular function) of cells than most invertebrates. Instead, they are filter feeders, meaning they obtain their food by straining the water for small bits of food like bacteria, algae or protozoans. Since they cannot move, sponges cannot pursue their food. All adult sponges are sessile, meaning they are attached to some surface.
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