The Echinoid Directory

Key to the genera of Strongylocentrotidae

1a. Ambulacra with four pore-pairs to a compound plate, forming vertical series.

1b. Ambulacral plates with between 5 and 10 pore-pairs to a compound plate.

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2a. Globiferous pedicellariae with paired lateral teeth and long muscular neck.

2b. Globiferous pedicellariae without lateral teeth and without muscular neck.

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3a. Ambulacra gradually narrowing towards peristome on oral surface; test thin.

3b. Ambulacral zones expanded adorally; broader than interambulacral zones at peristome edge.

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4a. Buccal notches sharp with well developed tag.

4b. Buccal notches feeble, hardly indenting the peristome and without tags.

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5a. Primary spines and tubercles large; spines with extensive median labyrinthic zone.

5b. Primary spines and tubercles not large; spines with well developed radial ridges.