Blue Zoo: Sponges
Featuring one amazing marine animal per week.
Sponges are all part of the Phylum Porifera, the most ancient and simple types of animals. They first arose about 500 million years ago – they make the dinosaurs look young!
Sponge bodies do not have tissues or organs. Sponges are merely groups of cells. Some sponges can even be disembodied - for example put through a blender or pushed through cheesecloth - and the cells will reorganize again afterwards! (Imagine trying that with any other type of animal...)
They are critical to ocean health for many reasons. They filter massive amounts of water, and feed on the particles in it, cleaning the ocean. Sponges are also important because they produce many chemical compounds with possible medical uses. Research on sponges has resulted in the development of the cancer drugs Halaven and Ara-C.
As you might have guessed from the name Porifera, sponge cell organization starts with pores. Sponges filter ocean water and feed on the particles they catch. This starts with porocytes, which cover the sponge. The water is carried through them to choanocytes, or collar cells, which catch the food particles with beating flagella (think tons of tiny tails). Filtered water then exits the sponge and re-enters the current through the osculum, a big opening at the top of the animal. You can watch this happen in this video.
Sponges also have spermatocyte cells for reproduction. They have cells for building a skeleton - sclerocytes secrete spicules of silica or calcium carbonate. They may have cells, called spongocytes, for producing spongin fibers. They also have archaeocytes; these are totipotent, meaning they can turn into any other type of cell, like human stem cells.
Although a handful of sponge species live in freshwater, almost all sponges are marine and live in the ocean. In spite of their simplicity, they have surprising diversity. Sponges can be anywhere from a few millimeters wide to larger than an adult person. While some sponges are soft and flexible like the one in your bathtub, others are made of delicate glass skeletons.