Crinoid

Crinoid

Crinoids are interesting marine invertebrates that belong to the class Crinoidea. They are part of a group called echinoderms. This group also includes starfish, brittle stars, sea urchins, and sea cucumbers. Crinoids live in both shallow waters and very deep oceans.

There are two main types of crinoids. One type stays attached to the sea floor with a stalk. These are called sea lilies. The other type is called feather stars or comatulids. Feather stars do not have a stalk when they grow up. Feather stars are the largest group of crinoids today.

Crinoids have a special way of eating. Their mouths are on the top of their bodies, surrounded by feeding arms. These arms have tiny branches called pinnules. The pinnules catch tiny particles in the water, called plankton. Crinoids have a five-fold symmetry, meaning their bodies are arranged in fives.

Today, there are about 700 kinds of crinoids in the ocean. In the past, they were much more common. Some thick limestone layers from the middle of the Paleozoic era through the Jurassic period are made from pieces of ancient crinoids.

Etymology

The name "Crinoidea" comes from an ancient Greek word for "a lily". This is why some crinoids are called sea lilies.

Morphology

Crinoids are special sea animals with a unique body shape. They have a stem, like a tail, and a crown made of a cup-shaped body and five arms that often branch out and look feathery. The mouth and anus are on the top of the cup, which is different from other sea animals like starfish and sea urchins. Their bodies are mostly made of small, hard plates, with only a little soft tissue.

Some crinoids, called sea lilies, use their stem to stick to the ocean floor. Other types, called feather stars, lose their stem when they grow up and can move around. Their arms have tiny parts called pinnules that help them catch food. These arms can curl up and have tiny feet to grab bits of food from the water.

Locomotion

Most modern crinoids, called feather stars, can move around. They crawl using their feather-like arms. They move to find better places to eat or to avoid other crinoids.

Crinoids can also swim by moving their arms. They swim upwards and then move sideways, traveling about 7 centimeters every second. They usually swim for short periods, like half a minute, to escape from something that might be dangerous. In 2005, scientists saw a crinoid move faster than before, sliding across the sea floor.

Main article: Florometra serratissima
Main article: Neocrinus decorus
Main article: Grand Bahama Island

Evolution

See also: List of echinodermata orders

Reconstructions of various extinct crinoids show what these sea animals looked like long ago. Crinoids first appeared about 480 million years ago during a time called the Ordovician. Scientists think they may have come from other sea creatures.

Crinoids were very common in ancient seas and changed a lot over time. They had two big bursts of growth, one during the Ordovician and another during the Triassic period about 230 million years ago. During these times, crinoids developed new ways to move and protect themselves. Some attached to floating wood, which later sank to the ocean floor, taking the crinoids with it. Today, we can find many crinoid fossils in rocks, showing how these interesting animals lived long ago.

Taxonomy

Crinoidea is a special group of animals called echinoderms. People have known about them since 1821. There are four groups of crinoids that are still alive today: Comatulida, Cyrtocrinida, Hyocrinida, and Isocrinida. All of these belong to a group called Articulata. Today, scientists know of about 540 different kinds of these living crinoids.

• Class Crinoidea
  • †Protocrinoidea (incertae sedis)
  • Subclass †Camerata
    • Order †Diplobathrida
    • Order †Monobathrida
  • Subclass Pentacrinoidea
    • Parvclass †Disparida
      • Order †Eustenocrinida
      • Order †Maennilicrinida
      • Order †Tetragonocrinida
      • Order †Calceocrinida
    • Parvclass Cladida
      • Superorder †Porocrinoidea
        • Order †Hybocrinida
        • Order †Porocrinida
      • Superorder †Flexibilia
        • Order †Sagenocrinida
        • Order †Taxocrinida
      • Magnorder Eucladida
        • †Ampelocrinida (incertae sedis)
        • Superorder †Cyathoformes
        • Superorder Articulata
          • Order †Encrinida
          • Order †Holocrinida
          • Order †Millericrinida
          • Order †Roveacrinida
          • Order †Uintacrinida
          • Order Comatulida
          • Order Cyrtocrinida
          • Order Hyocrinida
          • Order Isocrinida

In culture

Fossilized pieces of crinoids have been used as decorations for many years. In the Middle Ages, people in places like Lindisfarne made necklaces and rosaries from these fossils, calling them St. Cuthbert's beads. In the Midwestern United States, similar fossils are sometimes called Indian beads. One type of crinoid, Eperisocrinus missouriensis, is the official state fossil of Missouri. The design of the alien creatures in the Alien movie series was inspired by crinoids.

Fossil crinoid gallery

Here are some interesting fossils of crinoids from different times and places:

• Crushed crinoid stems from Shamshak Formation, Jurassic, Iran
• Fossil from Germany showing the stem, calyx, and arms with pinnules
• 330 million year old crinoid fossils from Iowa
• Crinoid holdfasts and bryozoans on an Upper Ordovician cobble from northern Kentucky
• Seirocrinus subangularis from the Early Jurassic Posidonia Shale at Holzmaden, Germany
• Crinoid columnals (Isocrinus nicoleti) from the Middle Jurassic Carmel Formation at Mount Carmel Junction, Utah
• Root-like crinoid holdfast from the Upper Ordovician, southern Ohio
• Internal mold of crinoid stem lumen (and external mold of stem) from Lower Carboniferous, Ohio
• Fossils of Seirocrinus subsingularis from the Jurassic Holzmaden Black Shale Formation, Germany
• Crinoid
• Some extinct crinoids, like Monstrocrinus from the Early to Middle Devonian, could have complex spines attached to their calyx plates