The Echinoid Directory

Key to the major clades of Scutellidea

1a.No lunules at any size.

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1b.Ambulacral notches or lunules present from a small size.

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2a. Anal lunule always present in posterior interambulacrum.

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2b. Anal lunule absent, ambulacral lunules or notches only.

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3a.Radial water canals and associated tube-feet extending far onto interambulacral areas; interambulacral zones at ambitus rarely less than 50% width of ambulacral zones.

Mellitidae

3b.Food grooves and pores for tube-feet confined to ambulacral areas; interambulacral zones tapering towards ambitus where they are usually less than 20% the width of ambulacral zones.

Monophorasteridae

4a.Lunules or notches festooned in construction; absent from posterior ambulacra. Interambulacral zones only ca. 20% width of ambulacral zones at ambitus.

Scutasteridae

4b. Lunules or notches cross-linked in construction; always present in posterior ambulacra. Interambulacral zones almost as wide as ambulacral zones at ambitus.

Astriclypeidae