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V. Vent Animals

The most abundant life at the vents, in fact some of the densest life on earth is found at these warm water vents. The organism that's certainly the most famous of all the vent organisms is Riftia pachyptila, the vestimentiferan tube worm. These worms get up to about a meter in length. They may be the fastest growing invertebrate. For those of you who subscribe to Science magazine, this week there is a photograph of this animal, not sitting on the deep sea floor, but sitting, thriving in Santa Barbara, California, in Jim Childress' laboratory. Childress has been able catch adults, bring them back, and keep them growing for weeks as long as they were fed a mixture of hydrogen sulfide and oxygen at the right concentrations. It's a worm that looks to have a mouth at its tip. But this red plume is actually a respiratory gas exchange surface. There is no digestive system in the worm. It's a worm whose food source comes from symbiotic bacteria that occur in an organ called the trophosome that fills most of the worm's body cavity. The worm itself, of course, is sitting in a white chitinous tube. These vestimentiferan tube worms are found only at the warm water vents. One doesn't find them in the black smoker water because its way too hot. One doesn't find them even slightly to the periphery of the warm water vents, where sulfide concentrations are too low to support the symbiosis.

Other species that are found in the warm water vents include a mussel called Bathymodiolus thermophilus and a variety of other invertebrates including Calyptogena magnifica a very large clam whose valve length can reach eight or ten inches. The distribution of these clams is very interesting. They show a very non-random distribution pattern. What they do is seek out cracks in the basalt. There are cracks that emit a tepidly warm water, water that's generally not as warm as the water in which one finds Riftia. What the clam does is to extend a foot down into that sulfide rich water. It thereby acquires sulfide in its blood. It picks up oxygen through its gills. In the gills are symbiotic sulfur bacteria. So the clam, like the big tube worm, is bringing in sulfide and oxygen and supplying them to sulfur bacteria in its gills. The sulfur bacteria cooperate. They basically "pay their rent" by releasing foodstuffs to feed the animal. Both Riftia and the clam are almost completely, if not completely, reliant on food material that's generated through chemosynthetic reactions in these symbiotic sulfur bacteria. (That's sort of a three minute version of what would have been a wonderful 50 minute talk by Jim had he been able to swim his way up here.)


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