The Echinoid Directory

Glossary

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Glossary terms beginning with: R

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radial water vessel
A baranch of the water vascular system that runs up the middle of each ambulacrum.
retractor muscles
Muscles connecting the pyramids to the perignathic girdle and used to pull the lantern into the test.
retractor muscles
rosette
Calcareous elements (usually five) that are arranged in a circle to form the frame of the suckered disc of tube-feet. (show image)
rostrate (pedicellaria)
A kind of pedicellaria with strongly curved blades that touch only at their distal tips. Not associated with poison glands. (show image)
rostrum
An anterior region of the test that is prolonged and projecting. The picture shows the cassiduloid Archiacia in lateral profile. (show image)
rotula
Part of the Aristotle's lantern. A bone-shaped ossicle that forms a brace between adjacent pyramids. It articulates with the epiphyses. (show image)