The Echinoid Directory

Glossary

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Glossary terms beginning with: O

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occluded plate
A small ambulacral element (blue) in a compound plate which does not contact the adradial suture. (show image)
ocular plate
One of the plates of the apical disc that lies perradially, at the apex of an ambulacrum zone. It is pierced by the tip of the radial water vessel. New coronal plates are added along its outer border. (show image)
ophicephalous (pedicellaria)
A pedicellaria characterised by having a prominent basal handle on each valve. (show image)
oral
The surface of the test bearing the peristome opening.
oral
orthofasciole
A fasciole in which clavulae (and their tubercles) are hexagonally close-packed, forming well-defined bands. This is the standard form of fasciole found in all extant atelostomates. (show image)