The Echinoid Directory

Key to the major clades of Spatangoida - 1

1a. One or more fascioles (partial or complete - indicated in yellow) present in adults.
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1b. No trace of fascioles present in adults (but may be present in juveniles).

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2a. Fasciole (marginal or subanal) crosses interambulacral plates 5.a.4 and 5.b.4 beneath the periproct.
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2b. No fasciole beneath the periproct in the posterior interambulacrum crossing plates 5.4. (A fasciole band crosses above the periproct above plate 5.8).

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3a. Fasciole forms a complete ring beneath the periproct (subanal fasciole).

3b. Fasciole extends around ambitus and crosses the lateral interambulacral zones (marginal/ lateroanal fasciole).


4a.Apical disc ethmophract.

4b. Apical disc ethmolytic.
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5a. Sternal plates asymmetric; labral plate not contacting plate 5.a.2.

Somaliasteridae (part)

5b. Sternal plates symmetrical; labral plate in contact with both sternal plates.