Choia carteri (a demosponge)
This unusual sponge, a small, thin disk with radiating spines, resembles a spiny sand dollar or a collapsed thatched hut. For a long time it was assumed that those spines in real life radiated upward and outward for protection (as with our present day sea urchins), but now we believe they actually laid out flat as shown. As a sponge, Choia would have laid on the substrate and filtered food particles out of the water. Moreover, lying with its convex side up as shown, it was less likely to be overturned by wave action. Size: about one inch in diameter.
Choia carteri (CHOY-ah CAR-ter-eye).
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