Extant spatangoids belong to one of three major clades, Hemiasterina, Micrasterina and Paleopneustina. All three have evidence of a late stage fasciole that forms after the periproct has begun migrating away from the apical disc - this is the peripetalous band that passes across plates 9-12 in interambulacrum 5. The Micrasterina and Paleopneustina both have an early formed fasciole on plate 4 (rarely plate 5) in the posterior interambulacrum that lies adoral of the periproct. In the Micrasterina this fasciole forms an enclosed subanal ring, and never extends into interambulacra 1 and 4. In Paleopneustina the fasciole is continuous around the test as a marginal fasciole. In some the marginal fasciole and peripetalous fasciole have coalesced anteriorly producing what is generally referred to as a lateroanal fasciole. However, in reality this is simply the posterior part of a marginal fasciole.
Despite having excellent data on the ontogeny of schizasterid fascioles, Mortensen (1950) failed to recognize that the lateroanal plus anterior portion of the peripetalous fasciole in schizasterids follows exactly the same plate path as the marginal fasciole in pericosmids. He separated both from the Paleopneustidae which he defined as primitively lacking fascioles. However, subsequently Chesher (1968) showed that juvenile Paleopneustidae possess both a marginal and peripetalous fasciole and that fasciole loss was secondary. The affinities of the three families Schizasteridae, Pericosmidae and Paleopneustidae was first recognized by Markov & Solovjev (2001).
Mortensen, T. 1950. A monograph of the Echinoidea V. Spatangoida 1. C. A. Reitzel, Copenhagen.
Chesher, R. H. 1968. The systematics of sympatric species in West Indian spatangoids: a revision of the genera Brissopsis, Plethotaenia, Paleopneustes, and Saviniaster. Studies in Tropical Oceanography 7, 1-168, pls 1-35.
Markov, A. V. & Solovjev, A. N. 2001. Echinoids of the family Paleopneustidae (Echinoidea, Spatangoida): morphology, taxonomy, phylogeny. Geos 2001, 1-109.
