The Echinoid Directory

Key to genera of Echinoida (2)

5a.Ambulacral plates trigeminate.

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5b.Ambulacral plating polygeminate.

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6a.Ambital interambulacral plate with single large primary tubercle. Test elongate along axis III-5.

Parasalenia

6b.Ambital interambulacral plates with two subequal tubercles. Axis of test elongation unknown.

Plagiechinus

7a.4-8 pore-pairs to a plate, arranged as a simple arc. Primary and secondary spines cylindrical.

Echinometra

7b.8-18 pore-pairs to a plate, often crowded so as to form a double irregular column. Primary spines stout and facetted.

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8a.Single large primary tubercle on all interambulacral plates.

Heterocentrotus

8b.Interambulacral plates at ambitus and above with two or more subequal tubercles.

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9a.Aboral spines stout and facetted, not forming a dense canopy; secondary spines not peg-like.

Zenocentrotus

9b.Aboral spines forming a dense canopy.

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10a.Aboral ambulacral plates with three equal tubercles. Aboral spines clavate.

Colobocentrotus

10b.Single large primary tubercle on aboral ambulacral plates. Aboral spines tesselated.

Podophora