The Echinoid Directory

Key to genera of Echinoida(7): Toxopneustidae

31a.Ambulacral plates trigeminate (3 pore-pairs to each compound plate).

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31b.Ambulacral plates polygeminate (4 or more pore-pairs to each compound plate).

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32a.7 or 8 pore-pairs forming oblique bands on each compound plate.

Pseudocentrotus

32b.4 or 5 pore-pairs forming oblique bands on each compound plate. Multiple subequal interambulacral tubercles.

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33a.Interradial and perradial bands devoid of secondary tubercles aborally (arrowed). Oral surface flat.

Pseudoboletia

33b.Aboral surface without naked interradial and perradial bands. Oral surface tumid.

Sphaerechinus

34a.Ambulacral pore-pairs arranged into three distinct vertical columns. Primary tubercles present on only every second to fourth ambulacral plate.

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34b.Ambulacral pore-pairs forming uniserial arcuate band or broad band. Primary tubercle on every ambulacral plate.

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35a.Interambulacral plates at ambitus with multiple equal-sized tubercles forming a horizontal series.

Toxopneustes

35b.Interambulacral plate with single primary tubercle and scattered smaller secondary tubercles; test rather naked.

Tripneustes