Sponges are considered the oldest animal phyla. They are multicellular but do not have tissues or organs.
The name porifera means ‘pore bearer’ in Latin. The surface of the sponge’s body is covered by a skin, one cell thick. This skin is penetrated by numerous small pores and a few large openings. The small pores are the entrances to a complex system of channels through which the sponge pumps a current of water from which its cells extract tiny particles of food. The channels lead to inner chambers lined with specialized feeding cells called a choanocytes or collar cells. On each collar cell a flagellum is surrounded by a ring- like a comb or collar; the beating of the flagellum draws water through the comb, where tiny particles are caught and carried down to the body of the cell to be digested. Food particles are taken in and digested inside the sponge's cells and the nutrients shared. This type of feeding is called filter feeding.
The body of the sponge between this system of canals is a loose assemblage of about six different types of specialized cells. Some of these cells secrete a supporting skeleton of collagen fibers or mineral spicules (glass or calcium carbonate). Collagen is a protein found in all animals that helps hold cells together and is a component of the skeletal system. Other specialized cells in the sponge carry out the processes of growth, repair, nourishment, or reproduction.
- Organized as an assemblage of different kinds of specialized cells
- No tissues
- Skeleton lacking or made of spicules
Porifera fact: Many sponges can filter their entire body volume in less than one minute.
Collagen: the main structural protein of the various connective tissues in animals; sponges, like all animals have collagen.
Spicules: structural elements found in most sponges that provide structural support, like a skeleton. Spicules can be made of silica or calcium carbonate.
Collar cell or choanacyte: these cells line the interior of the sponge.
Flagellum: a thread-like structure on the collar cells that whips back and forth, thus creating the current than pulls water through the sponge