description Hemicidaris crenularis Overview
Hemicidaris crenularis is an extinct species of regular sea urchin belonging to the family Hemicidaridae. The species was described from fossil material dating to the Jurassic period and has a taxonomic history linked to Lamarck's 1816 classification of Cidarites crenularis. As a regular echinoid, it possessed a rigid, globular shell covered in distinct tubercles that supported spines. These fossils are studied by paleontologists to understand marine ecosystems of the Mesozoic era.
help Hemicidaris crenularis FAQ
What kind of fossil is Hemicidaris crenularis?
Hemicidaris crenularis is an extinct regular sea urchin from the Late Jurassic, specifically the Oxfordian stage. The Smithsonian catalogs it as a Mesozoic fossil in the family Hemicidaridae. [Smithsonian fossil record](https://www.si.edu/object/nmnhpaleobiology_3136300)
Why is Hemicidaris crenularis linked to the name Cidarites crenularis?
Jean-Baptiste de Lamarck described the original species as Cidarites crenularis in 1816. Later taxonomic work placed that species in Hemicidaris, making the older Lamarck name part of the species' classification history. [Acta Geologica Polonica](https://journals.pan.pl/Content/81946/PDF/04_radwanska.pdf?handler=pdf)
What would a Hemicidaris crenularis fossil preserve?
A fossil may preserve parts of the hard echinoid test, the shell-like body, along with separate spine elements. It represents a Jurassic animal, not a living sea urchin species that can be collected from today's shoreline. [Smithsonian fossil record](https://www.si.edu/object/nmnhpaleobiology_3136300)
What does regular sea urchin mean in this species name?
Regular sea urchins have the familiar radial body plan associated with many modern sea urchins, rather than the flattened, bilaterally shaped form of sand dollars. Hemicidaris crenularis belonged to that regular group during the Oxfordian stage of the Jurassic. [Smithsonian fossil record](https://www.si.edu/object/nmnhpaleobiology_3136300)
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