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| teacher guide
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What
is a Crinoid?
page
10
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Crinoids
are often called "sea lilies" or "feather
stars". and are echinoderms (spiny-skinned animals) with
skeletal parts made of calcareous (limy) plates. They have
radial symmetry, digestive, nervous, reproductive and water
vascular systems. Their delicate arms strain tiny marine life
from the sea and move it toward its mouth.
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Some
crinoids are stationary, while others move freely over the ocean
floor or in floating mats. They may be found in all of the
oceans of the world and at vastly different temperatures and
depth.
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The
Crown includes the arms and the body, or calyx, of the
animal. The Calyx is the plate-covered body. It contains
the digestive systems and supports the arms, which help
gather food. The plates of the calyx are arranged in a
specific manner for each type of crinoid. Arms are the
long appendages that reach out from the calyx. Pinnules
are small extensions of the arms that help move water
and food to the mouth. The Stem is made of
individual disks with a central opening for nutrients
and nerve impulses. Free living crinoids often lack
stems.
Columnal,
or stem sections, is held together by flexible fibers
which allow movement. |
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Shape
and surfaces of the columnals may vary with each type of crinoid.
Cirri are the "arms of the stem" that hold the
crinoid to objects or the sea floor. The Hold Fast secures the
crinoid to the sea floor much like tree roots. Free moving
crinoids do not have hold fasts.
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This
slab holds the remains of crinoids and other invertebrate that
died on the Iowa sea floor 350 million years ago. At that time
Iowa was located near the equator and submerged under a warm
sea.
The
death of these animals was non-violent and their bodies drifted
into this depression to gently settle onto the limy mud. Layers
of lime covered their remains and preserved them from
destruction. When excavated their bodies lie randomly across the
stone and show no current or wave action.
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We
do not know why these animals died. Did the water temperature
rise? Did the salinity become change? Were they suffocated by
water that was too muddy ? We may never know.
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