The Echinoid Directory

Key to the families of Echinothurioida

1a. Peristomial membrane with 10 large buccal plates (arrowed) plus a few small marginal ambulacral plates.

1b. Peristomial membrane formed of a series of uniform, wedge-shaped ambulacral plates.

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2a. Primary spines ending in a conical hyaline hoof. Ambulacral pore-pairs arranged into three discrete columns in series.

2b. Primary spines simple, without a terminal hyaline hoof. Ambulacral pore-pairs forming a single irregular column in each series.

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3a. Ambulacra forming broad phyllodes adorally (peristome to right in picture), with larger and smaller primary tubercles forming multicompound elements.

3b. Ambulacra with uniserial pores adorally; primary tubercles not heterogeneous and not creating multicompound elements (peristome edge at far right).

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4a. Ambulacra with major element in each pseudocompound plate excluded from the adradial suture in ambital and adapical plates.


4b. Ambulacra with major element in each pseudocompound plate reaching adradial suture.