The Echinoid Directory

Key to the genera of Schizasteridae

1a. Apical disc ethmophract. Peripetalous fasciole passing vertically from plate 4 to plate 5 in interambulacral columns adjacent to the frontal ambulacrum.

1b. Apical disc ethmolytic. Peripetalous fasciole running across plates 4a and 4b in anterior interambulacra.

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2a. Apical disc with two gonopores only (gonopores absent from anterior genital plates).
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2b. Apical disc with three or four gonopores; the anterior sometimes reduced.

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3a. Apetaloid; adapical ambulacral plates rudimentary.

3b. Petaloid.

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4a.Petals deeply sunken and partially overarched so as to form only a narrow slit.

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4b. Petals modestly sunken at most and not overarched.
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5a. Sunken part of anterior ambulacrum short; not extending anterior of the paired anterior petals. Posterior petals less than half the length of anterior petals.


5b. Sunken part of anterior ambulacrum long; extending to the anterior of the ends of the anterior petals. Posterior petals only a little shorter than anterior petals.