The Echinoid Directory

Key to the higher taxa of Acroechinoidea

1a. Periproct lies outside the apical disc.

1b. Periproct encircled by the apical disc.

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2a. Teeth keeled.

Carinacea (includes Irregularia)
2b. Teeth grooved.

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3a.Pore-pairs uniserial at ambitus. aboral tube-feet simple.

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3b.Pore-pairs biserial at ambitus. Umbrella-like aboral tube-feet.

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4a. Apical disc (above) dicyclic and firmly bound to the corona; tubercles non-crenulate.

4a. Apical disc monocyclic or hemicyclic and rather weakly attached to corona; tubercles predominantly crenulate.

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5a. Apical disc (above) monocyclic and not firmly bound to the corona; with ocular plates larger than genital plates. Genital plates rectangular.

5b. Apical disc hemicyclic or monocyclic but integrated into the coronal plating and with genital plates projecting interradially into interambulacral zones. Ocular plates small.
6a.Primary tubercles crenulate; one primary tubercle per plate.
Pedinothuria (incertae sedis)
6b.Primary tubercles non-crenulate; multiple primary tubercles per plate.