Neognathostomata have traditionally been divided into a monophyletic Clypeasteroida and a paraphyletic Cassiduloida. Cladistic analysis (Smith 2001) suggests that cassiduloids are a grade taxon comprising a small number of clades leading to the Clypeasteroida. The majority of Jurassic cassiduloids belong to the common stem group of living cassiduloids plus clypeasteroids.
For a key to the modern species of Cassiduloida see Mooi (1990).
Mooi, R. 1990. Living cassiduloids (Echinodermata: Echinoidea): a key and annotated list. Proceedings of the Biological Society of Washington 103: 63-85.
- The following taxa are Neognathostomata but too poorly known to compare meaningfully:
- Anochanus Grube, 1869
- Echinanthopsis Munier-Chalmas, 1889
- Echinanthus Leske, 1778
- Heteronucleus Lambert, 1911
- Pseudonucleus Lambert, 1920
- Rostropygus Szorenyi, 1955
- Tropholampas Clark, 1923.