The Echinoid Directory

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Key to the genera of Apatopygidae

1a. Pyrinoid plating in ambulacra beyond petals (every second or third element small and restricted to adradial margin). Go to 2	1b.No pyrinoid plating in ambulacra beyond petals. Nucleopygus
2a.Four genital pores in a tetrabasal (juvenile) or monobasal (adult) apical system. Apatopygus	2b.Three genital pores in a tetrabasal apical system. Porterpygus