Great South Gems & Minerals

• Blastoid, Pentremites •
(Illinois)

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• Blastoid, Pentremites •
(Illinois)

Pentremites Blastoids - echinoderms - blastoids

Two well-formed Pentremites Blastoids in plastic bag with description card.

And extinct genus of stemmed, immobile echinoiderms (forms related to the starfish). 359 to 318 million years old. A genus of crinoids belonging to the Blastoidea. They have five petal-like ambulacra. Like most echinoderms, blastoids were protected by a set of interlocking plates of calcium carbonate, forming the theca. Blastoids show a very regular and tightly integrated plate arrangement, which is in part responsible for their abundance as fossils: the theca held together after the animal died.

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In life, the theca of a typical blastoid was attached to a stalk, or column, made up of stacked disc-shaped plates. The other end of the column attached to the ocean floor -- very much like stalked crinoids. The mouth was located at the tip of the theca. Radiating from the center like flower petals were five food grooves, or ambulacra. In life, each ambulacrum had many long, thin, fine structures called brachioles, which were used to trap food particles and bring them to the mouth.

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The living relatives including; starfish, sea cucumbers, sea urchins and brittle stars.

• See urchin
• See other blastoids

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