Activities

Objective: Students will learn that crinoids (phylum Echinodermata) are animals that filter feed plankton from the sea.

Problems to be solved: Can a student "build" a crinoid model that accurately portrays this relative to the starfish?

Supplies:

Disk-shaped beads

Stiff wire that will fit through beads

Foam-material

Feathers (smaller than 6-inches in length)

Water-filled aquarium(s) with at least 1-inch of sand on the bottom

Model clay (oil-based)

Instructions:

1.) String the disk-shaped beads on the stiff wire.

2.) Use foam material to create the body of the crinoid, its shape should be round, discoidal or cone.

3.) Trim feathers, which represent the arms of the crinoid. Insert them so that they have pentameral symmetry (5 equal angles). Use 5, 10, 15, feathers.

4.) Use clay, additional beaded wire or other creative method to anchor crinoid to the sediment. Let students determine how the crinoids should be anchored to the sediment. Let creativity rule!

5.) Place the model in an aquarium with sufficient water depth to cover the feather "arms"

Does their crinoid stay erect underwater? Does the holdfast hold?

Discussion: What methods of attachment did a crinoid use?

Disk holdfast, mangrove-root style, round bulb, grapple-hook anchor, whip-like to attach to the branches of colonial coral or bryozoans, some move like starfish.

Paleontologists call the root-like holdfast system "cirri "(an individual "rootlet" would be a "cirrus").

How did a crinoid column work?

If possible, look at an individual crinoid disk (called a columnal) or a clean specimen showing several stacked together.

Is the contact between them smooth or rough? Why would a rough surface between columnals be advantagous?

Look at the central hole (called the lumen) in a crinoid columnal. What is the shape?

Water circulated though the lumen carrying oxygen to the ligaments and tissue that kept the column intact. What carries oxygen to our muscles, ligaments and organs in our body?