The Echinoid Directory
Key to the major clades of Scutelliformes
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1a.Internal supports never more than simple radial struts; food grooves absent or rudimentary. |
1b.Internal supports developed as concentric bars, stellate patches or honeycomb mass after initial stages of growth; food grooves present. |
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2a.Food grooves an unbranched perradial trunk that extends across the most adoral two or three pairs of ambulacral plates (arrow marks edge of basicoronal plate). |
2b.Food grooves bifurcating at outer edge of first post-basicoronal ambulacral plate. |
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3a.Five gonopores. |
3b.Four gonopores. |
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4a. Food grooves bifurcating at second post-basicoronal plate. |
4b. food grooves simple or trifurcating at third post-basicoronal plate. |