We briefly covered sponges a few weeks ago in my Invertebrate Zoology class. It’s fascinating how they blur the line between what is a single animal and what is a colony of animals. These animals are not terribly complicated, but they do organize into beautiful repeating patterns in order to increase the efficiency of their food consumption. Though they don’t have organs or even tissues, a new study finds that they produce light-sensitive proteins.
There are four specialized cell types within a sponge. Choanocytes or collar cells, have a tiny flagella that they whirl around to create a slight current, and have a long, round net jutting off of the cell to filter the passing water. Pinacocytes form the walls, and porocytes allow water through the body. Archeocytes are the only cells which perform digestion, and sclerocytes’ sole purpose is to create structures of glass, spungin, or calcium carbonates to provide structure to the animal.
So nowhere in the system does this “animal” have any organs. It’s actually more like a bunch of bacteria that figured out an efficient way to organize themselves. But they are not bacteria, they are eukaryotes (they have true nuclei). But one would think they had not reached any more complex than a paramecium. While a paramecium is a single celled organism, it has specialized “organelles” which perform much like organs do for large animals. While the new article I found is quite vague, it represents a paradigm shift in the common understanding of sponges.
Check out the original story.