The Echinoid Directory

Family Schizasteridae Lambert, 1905, p. 154


  Paleopneustine spatangoids with:

  • periproct high on posterior truncate face;
  • anterior ambulacrum sunken, with differentiated pore-pairs bearing suckered tube-feet;
  • paired ambulacra petaloid, the posterior pair shorter than the anterior; sunken. No occluded plates at end;
  • labrum short and T-shaped; not extending beyond start of second ambulacral plate;
  • single fasciole crossing plates 4a and 4b in interambulacra 2 and 3, and plate 5 in interambulacra 1b and 4a. From plate 1.b.5 and 4.a.5 a semipetalous band rises to pass above the periproct and a marginal (lateroanal) branch passes posteriorly under the periproct. The lateroanal branch may be lost in development;
  • The fasciole crosses immediately around the base of the anterior petals.
Upper Cretaceous (Cenomanian) to Recent; world-wide.

The composition of this group is somewhat restricted in comparison to previous usage. The precise course of the peripetalous fasciole is highly conservative in this family and provides the key feature that distinguish this clade. Prenasteridae also have a single anterior fasciole but this crosses the anterior interambulacra on plate 3 and plate 4 in interambulacra 1b and 4a. Furthermore the fasciole passes two or more ambulacral plates below the ends of the petals.

The differentiation of many genera has been based on the presence or absence of the lateroanal fasciole and the number of gonopores developed. Both the loss of the lateroanal fasciole and the reduction of the anterior gonopores seems to have occurred several times independently and the monophyly of several of the genera is suspect.

The following taxon probably belongs to this family but is currently too poorly known to be meaningfully compared and is omitted from the key given below. It represents a nomen dubium

Hemifaorina Jeannet & Martin, 1937