The Echinoid Directory

Key to the major groups of cassiduloid, stem group Neognathostomata and stem group Clypeasteroida

1a. Ambulacral pores double on each plate.

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1b. Ambulacral pores single on plates beneath the petals.

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2a. Apical disc with Genital plate 3 always imperforate (two or three gonopores present).


2b. Genital plate 3 perforated by a gonopore (three or four gonopores).

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3a. Ambulacra with inner and outer series of pore-pairs in phyllode, the inner series on occluded plates.

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3b. Ambulacra with single irregular series of pores in phyllode; plating simple or with small adradial pyrinoid elements.

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4a. Periproct supramarginal, in anal sulcus.


4b. Periproct inframarginal to oral; flush.

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5a. Lantern and perignathic girdle absent in adults.


5b. Lantern and perignathic girdle present in adults.

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6a. Demiplates superficial; not penetrating through to interior of ambulacrum.


6b. Demiplates a fully integral part of the ambulacral zones.