Receptaculites

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Receptaculites, also known as "sunflower coral" or fossil honeycomb although it is not a coral or honeycomb, are a calcareous green algae that lived from the lower Ordovician to the Permian era. It formed a double spiral radiating pattern of rhombus-shaped plates supported by spindle-like meroms and grew on the seafloor. Fossils can usually be identified by the intersecting patterns of clockwise and counterclockwise rows of plates or stalk spaces. This fossil can be found in the Galena Group of minerals, which is presently not classified to any phyla.

Receptaculites fossils are found in two strata of rock layers in northern Illinois. They are also found in the Red River Formation (Ordovician) in the Williston Basin, with outcrops near Winnepeg, Canada. Believed to be a sea creature, this organism's structure has no known counter-part in living or fossil history.

The receptaculites are fossilized sea sponges from 450 milliom years ago.