The Echinoid Directory

Key to major clades of Clypeasteroida

1a.Pores confined to single adradial row. Sphaeridia not enclosed within plate.

Togocyamus (late stem-group clypeasteroid)

1b.Pores arranged as bands across plates as well as along sutures. Sphaeridia enclosed within plate.

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2a.Lantern muscle attachment structures on interior of test adjacent to peristome formed of paired ambulacral auricles (arrowed). Paired sphaeridia in each ambulacrum.


2b.Lantern muscle attachment structures single (fused), spoon-shaped and interradial in position. Single sphaeridium in each ambulacrum.