SpongePorifera

A sponge is an animal with no organs. No gut, no heart, no nerves, no muscle, and by most definitions no true tissue either. It has cells, and it has plumbing, and that is the entire design.

The plumbing is the point. Water is pulled in through thousands of pores across the surface, driven along internal canals by cells that each beat a single whip inside a collar of filaments, and pushed back out through the large opening at the top. A sponge moves many times its own volume of water through itself every hour and strains out particles far smaller than any fish can catch, bacteria included. On a reef this is not a footnote: sponges are a large part of the reason the water is clear enough to see coral in.

Break one apart and it puts itself back together. In an experiment more than a century old, a sponge was pushed through fine cloth until it was nothing but a suspension of single cells; the cells crawled toward each other, sorted themselves by type, and rebuilt a working sponge. There is no brain, no plan and no supervisor anywhere in that process.

What gives a sponge its shape is either glass or rope. Most species grow spicules, needles of silica or of calcium carbonate, locked into a scaffold; others rely on spongin, a tough protein fiber. A bath sponge is the spongin skeleton of an animal with everything else washed out of it.

An animal that cannot run or hide has to be unpleasant instead, and sponge chemistry has turned out to be unusually valuable. Latrunculin, now a standard laboratory tool for freezing the internal skeleton of a living cell, came out of a red finger sponge on this coast and was first pulled apart by chemists at the northern end of the 🌊 Red Sea. Fish that take a bite of that sponge do not take a second one.