The Echinoid Directory

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Key to the families of Cidaroidea 1a. Primary interambulacral tubercles surrounded by a differentiated circle of scrobicular tubercles. Go to 2 1b. Primary interambulacral tubercles without a differentiated circle of scrobicular tubercles. Ctenocidaridae 2a. Primary tubercles with rudimentary perforation or imperforate on at least the adoral plates. Peristomial membrane with ambulacral plates only. Psychocidaridae 2b. Primary tubercles with well developed perforation. Peristomial membrane includes non-ambulacral plates. Cidaridae