DK Nature: Sponges
These animals look like plants or fungi, but they are actually simple invertebrates. Most sponges dwell in salt water, spending their lives attached to rocks or reefs.
Sponges feed by drawing seawater in through pores in their surface and removing tiny plants and animals. Sponges lack the obvious body parts most animals have. They have no heart or other organs of any description. Sponges’ bodies are stiffened by tiny grains of limestone, silica, or a fiber called spongin.
This phylum includes about 5,000 species, divided into four classes:
| Calcareous sponges |
| Glass sponges |
| Demosponges (including the familiar bath sponge and tube sponges) |
| Scelerosponges |
