The Echinoid Directory

Key to genera of Arachnoididae

For alternative key see Mooi, R. 1989. Living and fossil genera of the Clypeasteroida (Echinoidea: Echinodermata): an illustrated key and annotated checklist. Smithsonian Contributions to Zoology 488, 1-51.

1a.Interambulacral zones separated on oral surface by a single enlarged pair of ambulacral plates.

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1b.Interambulacral zones separated on oral surface by three pairs of ambulacral plates.

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2a.Periproct opening aboral.

Fellaster

2b.Periproct opening oral.

Go to 3

3a.Periproct opening oral, bounded by first paired interambulacral plates.

Ammotrophus

3b.Periproct opening marginal, bounded by second paired interambulacral plates.

Monostychia