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- 1a. Ambulacral plate compounding in glyphocyphid style.
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1b. Ambulacral plate compounding in echinid style. - Go to 4
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2a. Primary tubercles perforate. - Glyphocyphidae
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2b. Primary tubercles always imperforate.
Go to 3 |
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3a. Apical disc monocyclic.
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3b. Apical disc hemicyclic.
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| 4a. Test ornamented by pits or epistromal ridges (may be lost in adults) Go to 5 |
4b. Test unornamented; no pits or epistromal ridges at any stage.
Go to 6 |
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5a. Ornament consists of sharp-edged sutural pits.
Temnopleuridae |
5b. Ornament consists of raised epistroma or tuberculation with irregular depressions, some of which are sutural.
Trigonocidaridae |
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6a. Apical disc monocyclic.
Triplacidiids |
6b. Apical disc hemicyclic to dicyclic.
Go to 7 |
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7a. Tubercles crenulate.
Porosoma |
7b. Tubercles non-crenulate.
Go to 8 |
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8a. Buccal notches deep and sharp.
Toxopneustidae |
8b. Buccal notches obsolete.
Echinoida, Pseudechinus |