Sea sponges belong to the phylum Porifera, which means pore-bearing animals. All members of this phylum are aquatic. Sponges lack mouths; instead, they use pores to take in food from their watery environment. Poriferan fossils are some of the oldest animal fossils ever found, dating back to the Precambrian period, about 600 million years ago.
All sponges are aquatic bottom-dwellers. Sea sponges all live in marine environments, but a single family of phylum Porifera lives in fresh water. Sea sponges are also sessile, meaning they stay in one place and cannot move on their own. While observers have seen some sponges move up to four millimetres per day in an aquarium, they have not viewed this behaviour in their natural environment. (2)
Sea sponges have specialised cells that carry out different body functions. Sponges have a simple body design. Unlike more complex animals, they have no cells organised into tissues and organs. This type of system is cellular-level organisation. Members of phylum Porifera are parazoans; they are different from other groups of animals because they lack true tissues and do not have body symmetry.
A skeleton consisting of spicules supports a sea sponge's body and gives it shape. Spicules are strong materials such as mineralised calcium carbonate or silica, or the protein spongin. They form a network of hard, interlocking branches. Spicules make up the fossilised remains of sponges. Collagen also supports sponge bodies.
Pores and Feeding
All sea sponges have pores called ostia that allow water to enter. Water pumps through a canal system to an open space within the sponge's body called a spongocoel. From there, water exits the sponge through openings called oscula. Cells called choanocytes have tail-like structures that whip back and forth to cause the pumping action within the sponge. These cells also collect nutrients from organic matter in the water pumped through the sponge's body. Archeocytes digest the nutrients and transport them to other cells within the sponge.
- University of California Museum of Paleontology: Porifera, Life History and Ecology
- University of California Museum of Paleontology: Porifera, More on Morphology
- Kennesaw State University: Porifera
- University of Michigan Museum of Zoology: Animal Diversity Web, Porifera
- University of California Museum of Paleontology: Introduction to Porifera