Archaeocidaris occured in large groups since the environment included plenty of food and protection from waves and currents. Like modern sea urchins, living in groups improves spawning and provided protection. Once the first sea urchin was found at this fossil site the search was on for more. Dozens of additional specimens were collected.
Archaeocidaris had a spherical, calcareous skeleton or test made of moderately thick plates that were arranged radially in two types of double columns. The first double column, termed the ambulacrum (plural-ambulacra), had two pores in each plate for the projection of tube feet. Hydraulically powered tube feet aid in locomotion, anchoring, feeding, sensing the environment, and respiration.
|Polygonal interambulacral plates that form part|
of the Archaeocidaris test. Spines fit on the large knobs
or tubercles in the center of the plates.Spines are
rarely preserved as fossils.
|The interambulacral plates have conspicuous bumps in |
the center where the spines were once connected.
Because sea urchins are generally one of the first marine organisms to show signs of stress if something is wrong with the water, the Environmental Protection Agency uses them as an indicator organism for water quality near shores and in bays. When conditions are poor, sea urchins will stop moving, their spines will droop, and they will die.