The Echinoid Directory

Key to the genera of Prenasteridae


1a. Frontal groove clearly developed.
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1b. Anterior of test flat to convex.

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2a. Apical disc with three gonopores.

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2b. Apical disc with four gonopores.

3a. Anterior and posterior petals subequal and obviously sunken
Tripylus

3b. Anterior petals much longer than posterior petals and both only slightly depressed.

Cagaster

4a. Apical disc subcentral or slightly posterior of centre; petals cruciform, the posterior less than half the length of the anterior.
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4b. Apical disc markedly anterior; anterior petals almost at 180 degrees and almost as long as the posterior petals.

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5a. Pores in the anterior column of the anterior petals are entirely rudimentary.

Agassizia

5b. Pores in the anterior column of the anterior petals are rudimentary only in the upper part.

Anisaster

6a. Lateroanal part of marginal fasciole absent. Aboral tubercles heterogeneous.

Unifascia

6b. Lateroanal part of the marginal fasciole present. Aboral tubercles fine and uniform.

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7a. Posterior strongly undercut; periproct very large.

Brissomorpha
7b. Posterior vertically truncate; periproct relatively small at top of truncate face
Prenaster