Blastoids
The blastoids (blas'-toids) are stemmed forms with pronounced five sided (pentaradial) symmetry and are commonly called “sea buds.”
See below.
Fossil blastoids in matrix. These come from the eastern USA. Photo taken by DanielCD on 4/19/05.
These “buds” are the most commonly preserved part of the animal - it has the general shape and approximate size of a rosebud.
In A and B below, the areas noted as ambulacral are specialized and would bear numerous food-gathering brachioles (See C).
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In a side view, you see what the Brachioles would look like sprouting from the ambulacral, the name of the radial plates, called Theca, its column, and like a crinoid, a root structure called a “hold fast.”
 The structure of a blastoid:
A) Side view of the calyx of the Mississippian blastoid, Pentremites (Prothero, 1998);
B) Top view of the same blastoid (Prothero, 1998);
C) A generalized blastoid from the Carboniferous (Brusca, 1990).
If you are familiar with Crinoids, you will see that Blastoids are closely related. However, inside of the arms like a Crinoid, Blastoids had long hair-like brachioles that swept food into the mouth. Because the brachioles were so delicate, they are rarely preserved. |
Like Crinoids, blastoids had a mouth at the top of the body, called a calyx surrounded by small round holes that conducted food particles into and wastes out of the body.
The oldest blastoids, found in Silurian rocks, lived about 425 million years ago. They survived until the Permian Period, about 260 million years ago, when they became extinct.
Blastoids are beautiful fossils that look much like small hickory nuts.
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