also called sea lilies, are relatives of starfish and sea urchins. Crinoids were animals attached to the sea floor by
flexible, rooted stalks. They spend most of their time
standing around and catching food. When they died, they usually broke loose and drifted away. The
crinoid fossils found in the Legrand Quarry are remarkable because many of them were
preserved nearly intact. The reason this happened is that nests of crinoids were rapidly
buried in shallow depression that protected their bodies from currents. Lime-rich mud
preserved their remains and hardened them into stone. The limestone slabs found near
Legrand contain fossilized crinoids and other sea animals in such abundance and detail
that they have fascinated scientists around the world.
360 million years ago (in the Paleozoic era or Mississippian period) North America was located near the equator. Much of the land - including what's now Iowa - was submerged under shallow tropical seas. These warm waters teemed with countless creatures.
The inland seas reportedly swelled and retreated, alternately building up and exposing layers of sediments, sandwiching the remains of crinoids and other living things, and casting their impressions in stone.
Crinoids, commonly called "sea lilies" or "feather stars," belong to the echinoderm family (bodies covered with plates of calcite that form a skeletal structure) along with starfish, sand dollars, sea urchins, and sea cucumbers.
Some crinoid species crawled, some swam, and others attached themselves to rocks on the sea floor. They fed by means of cilia, located along grooves in their arms and branches, that brought tiny marine life to the mouth. Today, crinoids live in all the world's oceans, and where they're found, their abundant numbers and vibrant colors give the appearance of an underwater flower garden.
Crinoids have cup-shaped bodies with at least five feathery arms atop column sections that form cylinders and spirals. These shapes seem to radiate from a central point. This is called radial symmetry.
Animals get food directly from plants or other animals that eat plants. Crinoids are animals because they eat other marine life. Each featherlike arm that radiates from the central body bears an open ambulacral groove bordered by tube feet. The longest tube foot is held out at a right angle and flicks passing food particles into the groove. After a food particle is captured by a crinoid, the shortest tube foot wraps it in mucous secretions; ciliary tracts on the groove floor then transport it toward the mouth. Diets include a variety of protists, invertebrate larvae, and small crustaceans.
Scientists have known for a while that some stalked crinoids move. But they usually creep along so slowly that it's hard to tell they're actually going anywhere. Previously, researchers aboard submersibles had noticed that crinoids appeared in different positions from dive to dive. Still, the creatures had never been measured moving faster than about 0.6 meter per hour (2 feet per hour).
Now, analysis of an old video has revealed a record-breaker. In the 1990s, a submersible off Grand Bahama Island filmed a stalked crinoid moving at a speedy 140 meters per hour (459 feet per hour). The video was taken at a depth of about 400 meters (1,300 feet). It showed the creature lying on the bottom, pulling itself along with its arms. It's the sort of crawling you might do using your elbows to pull you along.
Researchers suspect that crinoids "run" to get away from hungry predators.