Hemicidaris

Echinoid

Middle Jurassic-Upper Cretaceous

This regular echinoid has a radially symmetric, hemispherical test (approximately 3 cm in diameter). The ambulacra are narrow and the plates are ornamented with small tubercles. The interambulacral plates have a large, central tubercle surrounded by smaller, less prominent tubercles. A long, solid, primary spine was articulated on the central prominence and shorter spines attached to the minor tubercles. Spines were used for protection and locomotion. Such regular echinoids were epifaunal and lived in shallow marine and intertidal environments.

Clypeus

Echinoid

Middle-Upper Jurassic

This irregular echinoid has a flattened, bilaterally symmetric, discoidal test with a rounded outline (diameter approximately 6 cm). Ambulacral areas are expanded into the full petaloid condition with slit-like pores. The anus is situated within a pronounced groove on the aboral surface. The mouth is at the center of the oral surface. Clypeus was an infaunal echinoid. The ribbon-like tube feet were adapted for respiration.

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