First, an update. This week which is early April 2014, scientists from China, England, and the United States announced a new discovery from the Chengjiang faunal of China. Those are the remarkably well preserved Cambrian fossils that we talked about on February 8.
The report details an arthropod that’s so well preserved, they have been able to describe the animal’s cardiovascular system. I’ve put a link to this paper on the February 8 episode.
Crinoids are echinoderms whose plant-like appearance gives then the name “sea lilies,” but they are animals related to starfish. And the name itself comes from the Greek word for a lily. Crinoids originated during the Ordovician biodiversification, but they expanded dramatically during the Silurian. As fossils, their disk-like segments, from their stems, are really common. Their more fragile, cup-shaped calyxes, where the animal’s feeding and digestive organs were located, are more rarely preserved. But when they are, they are some of the coolest fossils around.
Most crinoids were attached to the sea floor, though a few were free-floating, and most of the modern species are free-floating as well. The sea-floor attachments are called "holdfasts," but they really do look like the root system of a plant.
—Richard I. Gibson
Crinoid drawn by James Hall (1881). Natural height about 5 inches.