The Echinoid Directory
Key to major clades of Clypeasteroida
 |
 |
|
1a.Pores confined to single adradial row. Sphaeridia not enclosed within plate. |
1b.Pores arranged as bands across plates as well as along sutures. Sphaeridia enclosed within plate. |
 |
 |
|
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. |