Thursday, February 4, 2010

Ancient sea lily remains: St. Cuthbert's beads

Sea lilies, also known as crinoids, are marine animals: echinoderms related to starfish and sea urchins. Stem and branches of a sea lily are built as a stack of disk-shaped, calcareous plates. Each plate features a central hole in such a way that a fluid-filled canal can run through the inside of the stack (or stalk), allowing the passage of a nerve cord. The separated plates of fossil sea lily stalks are called St. Cuthbert's beads, named in the 17th century by English naturalist John Ray and Thomas Willisel of the Royal Society after Saint Cuthbert (ca. 634-687), bishop of Lindisfarne in northeastern England [1]:
The two men “gathered on the sea-shore under the town [on Lindisfarne island], those stones which they call St. Cuthbert's beads. ” The “beads,” which ranged in size from the diameter of a pea to that of a half dollar, were the ridged and perforated fossil disks of stalked crinoids, or sea lilies.
According to today's knowledge, the “beads” found by Ray and Willisel originate from sea lilies that were living in a warm, shallow sea bed between 363 and 325 million years ago, when northern England was near the earth's equator.

Keywords: Echinodermata, Crinozoa, Crinoidea, crinoid stalks, paleontology, history

[1] Anna Marie Roos: Lilies of the Sea. Natural History December 2009 / January 2010, Volume 118, Number 10, pp. 26-30.
[2] N. Gary Lane and William I. Ausich: The Legend of St Cuthbert's Beads: A Palaeontological and Geological Perspective. April 2001. BNET-Article.
[3] Natural History Museum: Fossil Folklore, Crinoids: St Cuthbert's Beads.

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