WE WERE descending through the Caribbean sea in a tiny submarine. Our mission: to go down more than 200 metres to hunt for living fossils called stalked crinoids.
Crinoids are like upside-down starfish. But whereas starfish crawl over the sea floor, their relative, the crinoid, is rooted to the bottom via a stalk. Crinoids 鈥� also known as sea lilies 鈥� thrust as many as 60 feathery arms upwards to strain plankton from the water. About 300 million years ago, when the seas were just a soupy mixture of plankton with no fish or mammals, the crinoid was king. But as their environment changed, extinction loomed.
Around 200,000 years ago, a new subclass evolved with the ability to move. There was an explosion of new species, and most of the stalked, stationary ancestors became extinct. Shale beds 鈥� the muddy bottoms of ancient seas turned to rock 鈥� are covered with dime-size circles, the fossilised remains of crinoid stalks. Only about 80 species survived, all relegated to the deepest recesses of the ocean, where they eke out a meagre existence. Their metabolism is so slow that they can live for a thousand years. We wanted to see these animals in the flesh.
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We began near Jamaica, descending with the submarine鈥檚 bow about a metre from the island鈥檚 continental slope. On the way down, we made a surprise discovery. In a depression, I saw what few people have seen. My heart raced. It wasn鈥檛 the crinoids we were searching for, but I immediately recognised this object as the rarest of finds. There in front of me was what appeared to be a woman鈥檚 breast. It was in fact the rounded mass, complete with 鈥渘ipple鈥�, characteristic of Ceratoporella, a member of an obscure, newly described class of sponges, Sclerospongia.
I never thought I would see a live Sclerosponge. Ceratoporella nicholsoni is rarely found above 60 metres, well beyond the scuba-diving capacity of all but a few brave souls. The person who first discovered this species found the specimen in a cave close to maximum diving depth. We were seeing this sponge class in the open, perhaps one of the first such viewings.
We continued our slow descent. The wall became a slate-grey desert, and occasionally we came too close and disturbed the silty surface, producing a puff of fine sediment which had hadn鈥檛 been touched for thousands of years. Then the whining of the motor slowed and we felt a bump. 鈥�740 feet,鈥� announced the submarine captain. He shut off the power. The lights went out and we were alone in 鈥渋nner space鈥�.
The captain turned on the lights to reveal another surprise. On a rock nearby were five stalked crinoids 鈥� a veritable garden. This was the first time I had seen these relics of another era alive, instead of in a lab specimen jar. We had seen two of the rarest organisms on Earth. Not bad for a day鈥檚 dive.
