The Echinoid Directory

Key to the families of Micrasterina

1a. Episternal plates (in red) paired and opposite. Subanal fasciole (where developed) crossing middle of episternals. Apical disc ethmolytic.
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1b. Episternal plates (in red) distinctly staggered at rear. Subanal fasciole (where developed) crosses sternal-episternal boundary. Apical disc ethmophract.

2a. Labral plate (yellow) elongate and wedge-shaped; extending to at least half way down the second ambulacral plate.
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2b. Labral plate anvil-shaped; wider than long; not extending beyond the first ambulacral plate.

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3a. Anterior ambulacrum flush and narrow; without specialised funnel-building tube-feet and enlarged pore-pairs.
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3b. Anterior ambulacrum sunken and with specialised aboral funnel building tube-feet and enlarged pore-pairs.


4a.Petals well developed; always narrow and parallel-sided. Peripetalous fasciole always present.

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4b. Petals poorly developed or absent. No peripetalous fasciole.

5a. Petals narrow and parallel-sided.


5b. Petals distinctly bowed or lanceolate with wide interporal zone.