The Echinoid Directory

Glossary

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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.
rosette: Calcareous elements (usually five) that are arranged in a circle to form the frame of the suckered disc of tube-feet.
rostrate (pedicellaria): A kind of pedicellaria with strongly curved blades that touch only at their distal tips. Not associated with poison glands.
rostrum: An anterior region of the test that is prolonged and projecting. The picture shows the cassiduloid Archiacia in lateral profile.
rotula: Part of the Aristotle's lantern. A bone-shaped ossicle that forms a brace between adjacent pyramids. It articulates with the epiphyses.