The Echinoid Directory

1a. Ambulacra biserial throughout, with oral plates much larger than aboral plates.

1b. Ambulacra partially (adorally) or entirely multiserial.

2a. Ambulacra uniserial over aboral surface, expanding markedly just above ambitus and becoming multiseria adorally.

2b. Ambulacral plating multiserial over aboral surface.

3a. Ambulacral plates large and biserial on oral surface, becoming quadriserial at ambitus; small perradial flanges roof radial water vessel adorally.

3b. Ambulacra multiserial throughout.

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4a. Adoral ambulacral plates with a mixture of large circular pore-pairs and small undifferentiated pore-pairs.

4b. Adoral ambulacral pore pairs all large and circular.

5a. Interambulacra reduced to a single column of plates on oral surface and completely absent from adoral region.

5b. Interambulacra remain multiserial to basicoronal plate adjacent to peristome.