![]() |
![]() |
1a. Test composed of more than 20 columns of plates (more than 2 ambulacral or interambulacral columns in each zone) |
1b. Test composed of just 20 columns of plates; interambulacral and ambulacral zones each composed of two columns of plates |
![]() |
![]() |
2a. Test with bilateral symmetry superimposed over pentaradial plan; periproct displaced to the posterior - almost always lying outside the apical disc plates. |
2b. Pentaradially symmetric; periproct opening surrounded by circlet of apical disc plates |
|
![]() |
3a. Perignathic girdle rudimentary or absent. |
3b. Perignathic girdle well developed, composed of ambulacral auricles and/or interambulacral apophyses. |
![]() |
![]() |
4a. Perignathic girdle always present and composed of interambulacral apophyses (ap) only. Ambulacral plating simple and extending onto the peristome. |
4b. Perignathic girdle composed of ambulacral auricles (au). Ambulacra always compound. |