Blastoid Pentremites sp.

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Pentremites are extinct echinoderms that closely resemble crinoids. They, too, were stalked and grew to an average of 5 inches tall. Blastoids like Pentremites lived on the ocean bottom using their lengthy appendages to capture food particles around 325 million years ago.

The nut-shaped theca of the Pentremites is a set of interlocking plates of calcium carbonate that preserved the animal after death. The mouth was at the tip of this theca and the five tentacle-like ambulacra lined with fine structures called brachioles trapped food and directed it to the mouth. The five holes surrounding the mouth serve a purpose--the largest hole is the anus and the others are the start to the respiratory organs called hydrospires.

Pentremites sp.
Ridenhower Formation
Floraville, Illinois


Size (of plate): 3.63 x 2.44 x .63 inches

Size (of largest specimen): .69 x .44 x .31 inches

Weight: 1.9 oz.