Types

• There are four classes of sea sponges: Calcarea, or calcerous sponges; Demospongiae or horn sponges; Scleropongiae or coralline tropical reef sponges; and Hexactinellida or glass sponges. It is difficult to pin down the exact number of sponge species as many distinctive species have been named more than once and new species continue to be found. While there are close to 10,000 different names for species of sponges, it is more likely that there are about 6,000 actual different species.
  
  

Anatomy

• The body of a sea sponge consists of a pair of outer layers that are separated by a gel, or the mesenchyme. Needles formed from calcium carbonate (spicules) or flexible protein skeletons (spongin) are found within the gel layer to help the sponge maintain its form. Sponges do not have organs or tissues. They are made up of pores that allow the constant flow of water in and out, which in turn provides oxygen and nourishment as well as the elimination of waste. Sponges are found in a wide variety of shapes, from blob-like formations to cones and tubes, and vary in size from as small as a few millimeters to as much as two meters in height.
  
  

Diet

• Through their thousands of pores, sea sponges filter food from seawater. Sponges eat plankton and other tiny organic material found in the water. Choanocytes, or collector cells, take in nutrients and carry them to amoebocytes, which break down food and distribute energy to the rest of the sponge.
  
  

Reproduction

• The majority of sea sponges are hermaphroditic, meaning that sponges contain both eggs and sperm. While it is possible for a single sponge to fertilize its own egg, more often, sperm is released from a sponge and then floats randomly in seawater to be "caught" by another sponge. Once an egg is fertilized inside of a sponge, the sponge releases larvae into the water. The larvae settle on the sea floor to grow into a new sponge.
  
  Some types of sponges reproduce in an asexual manner to create clones. In this form of reproduction, buds, or fragments of the sponge body, break off and float in the sea currents. These buds settle on the sea floor to grow into a sponge identical to the parent.
  
  

Natural Bath Sponges

• There are only about six species of sea sponges that are sold commercially as bath sponges. These species are selected for their dense make-up and flexible skeleton. In their natural environment, these sponges are black; however, they are placed into mildly acidic solutions to decalcify the skeletons and then bleached to remove color.