Receptaculites

Receptaculites is the name-bearing genus for an extinct group of conspicuous benthic marine genera, the Receptaculitidae, that lived from the Early Ordovician through the Permian period, peaking in the Middle Ordovician. The group's phylogenetic origin has long been obscure, but the current understanding is that the Receptaculitidae were calcareous algae, probably of the Order Dasycladales. Receptaculitids lived in warm, shallow seas and have been described from all continents except Antarctica. In some areas they were important reef-formers, and they also occur as isolated specimens.
"Receptaculites" and its relatives have a double-spiral, radiating pattern of rhombus-shaped plates supported by spindle-like objects called meroms. Fossils can usually be identified by the intersecting patterns of clockwise and counterclockwise rows of plates or stalk spaces, superficially similar to the arrangement of disk florets on a sunflower—hence the common name "sunflower coral" ("sic").